The world has rallied around France in the wake of gruesome simultaneous terrorist attacks on the capital Paris, whose death toll last evening had reached at least 127 people, with dozens more critically injured.

France President Francois Hollande declared war on the so-called Islamic State (IS) terrorist group, which claimed responsibility for the attacks in five different locations.

The attacks took place on Friday evening, with most casualties reported at a concert hall where Eagles of Death Metal, an American rock band, was playing to thousands and outside the Stade de France, the stadium where the French and German national football teams were playing a friendly match.

Other attacks were at bars and restaurants. AFP, a French news agency, reported that at least 300 people were hospitalised after the attacks, 80 of them in "critical" condition.

On Saturday, President Uhuru Kenyatta sent a message of solidarity with the French people while the Inspector-General of Police Joseph Boinnet called for vigilance.

"As a nation that has suffered similar outrage, we understand that the attacks in Paris must be met with the strongest action by our security forces. Kenya stands ready to offer every assistance possible in this regard, and indeed we will continue to relentlessly prosecute our war against terrorist groups and their support networks," said President Kenyatta.

He added: "Beyond the critical security interventions being made presently by the brave soldiers of France, I urge all Kenyans and indeed the entire global community to stand up and loudly rededicate ourselves to the common values all civilised people hold."

Deputy President William Ruto tweeted: "I am saddened by the terror attack in France.This is an attack on humanity. As nations we must unite to defeat this enemy."

Cord leader Raila Odinga, who is out of the country, said he stood in solidarity with France and Lebanon--which also suffered a terror attack claimed by IS.

"I stand in solidarity with the people and the leadership of both nations. Our thoughts and prayers go out to families of those who have lost loved ones. The world now more than ever needs to speak with one voice against terror," he said.

Cord co-principal Kalonzo Musyoka sent "Kenya's thoughts, prayers and resolute solidarity" following the brutal attack.

AN ACT OF WAR
Mr Boinnet said security levels had been raised. "Whilst we in the police have stepped up vigilance, we call on the public to exercise maximum levels of alertness. Report any suspicious activity and/or persons to the police or any security agency for action. Let’s work together to protect our motherland."

Kenya has in the past suffered deadly Al-Shabaab terrorist attacks, including at the Westgate Mall in 2013 and Garissa University this year.

In Paris, it was unclear if there were any Kenyan casualties but the Foreign Affairs ministry indicated all its staff in the European city were safe.

On Saturday, President Hollande declared the attack was an act of war: "France will be ruthless in its response to Islamic State."

The President himself had to be evacuated from the stadium after some of the attacks were staged within earshot.

"What happened yesterday in Paris and Saint Denis is an act of war and this country needs to make the right decisions to fight this war. This act committed by the terrorist army, Islamic State, is against who we are, against a free country that speaks to the whole world," he said in an address to the nation.

He also declared three days of national mourning and called for unity ahead of his address to Parliament on Monday.

BBC reported that they were "the deadliest attacks in peacetime France, and only the fourth time since WWII that a state of emergency has been imposed. The last time was during a 2005 wave of riots in poor suburbs. It is the worst atrocity in Europe since the 2004 Madrid bombings."

In a statement posted online Saturday, IS said "eight brothers wearing explosive belts and carrying assault rifles" conducted a "blessed attack on---Crusader France."

Survivors described fleeing over bodies after the gunmen began executing rock fans in a barrage of automatic gunfire.

"It was horrible inside, a bloodbath, people shot in the head, people who were shot as they were lying on the ground," said a police officer who took part in the operation to storm the venue where 1,500 people had been attending a rock concert.

IMPROVE SECURITY
At least 82 people were killed in the concert hall by four black-clad attackers who opened fire with automatic weapons on the packed venue, sowing carnage and panic.

"At first we thought it was part of the show but we quickly understood," said radio presenter Pierre Janaszak who was sitting in the balcony with his sister and friends when they heard shots from below about an hour into the concert.

"They didn't stop firing. There was blood everywhere, corpses everywhere. We heard screaming. Everyone was trying to flee."

They hid in a toilet where they would spend the next two hours waiting for police to storm the building as the terrorists held hostages.

"I clearly heard them say 'It's the fault of Hollande, it's the fault of your president, he should not have intervened in Syria'," he said.

Mr Stephen Kinuthia, a Kenyan living in Paris, told the Sunday Nation that he was at a restaurant 500 metres away from the 1,500-seater Bataclan concert hall when they first heard what sounded like a tyre burst.

"We could hear it from very far and, after some time, we saw the police vehicles and ambulances passing outside. The owner of the bar then asked everybody to leave as there was a terror attack," he said on the phone.

Mr Kinuthia said that with the subway (underground trains) and taxis nowhere to be seen, he walked towards the scene, which was also in the general direction of his house.

"The police, the journalists there and everybody was getting messages about the other attacks and people were very agitated," he said.

Mr Kinuthia said he lingered at the scene for some time, taking photos, sending messages to his friends and family in Kenya and in France before eventually taking a circuitous route home because many streets were blocked.

He asked the Kenyan authorities to step up security at its embassies abroad because the country's involvement in Somalia makes it a target for attacks.

The day after the bloodbath, major attractions in Paris were shuttered from Disneyland and the Eiffel Tower to the Chateau of Versailles, and its picturesque squares and avenues were eerily quiet.

SECOND TERRORIST ATTACK
Schools, markets, museums and other tourist sites across the greater Paris area were closed and sporting fixtures were cancelled on the orders of the city or national authorities.

Only civil registration offices, to record marriages, will be open, city officials said, adding that security would be beefed up at town halls.

In the Place de la Bourse, a large square near the Paris Opera, traffic was unusually thin and pedestrians were few.

"People are worried," Jean-Louis Masson, 50, who lives locally, told an AFP reporter.

"You can see that in the SMS messages that are going around. We were concerned for one of our children who was out last night, and we called to make sure she came home."

Police said all public demonstrations in the Paris region would be banned until Thursday.

A line of people at least 100 metres long formed outside the city's main blood donation centre, even though no appeal had been made.

Outside a Cambodian restaurant where 12 people were killed, mourners placed flowers, a candle and the French national flag, which had written on it "Fluctuat nec mergitur"---the Latin slogan of Paris, which means "It is buffeted by the waves, yet remains afloat."

It was the second terrorist strike in less than 10 months. In January, 17 people were killed in jihadist gun attacks, five of the cartoonists at the satirical magazine Charlie Hebdo. 

At newspaper kiosks, dramatic headlines and pictures likened Paris to a combat zone, after suspected jihadists attacked crowds and restaurants goers.

"War in the heart of Paris," the conservative daily Le Figaro said. "This time, it's war," Le Parisien said.

Separately, the French secretary of state for sports issued instructions to sports federations to cancel matches this weekend.

Cancelled events include a European Champions Cup rugby match between Racing 92 and the Glasgow Warriors.

TERRORISM'S BABARITY

Even as the messages of support poured in from across the world, the attacks sparked security alerts in London's Gatwick Airport.

The North Terminal at the airport was evacuated on Saturday due to "an incident".

Sussex police later confirmed they were dealing with a "suspect package".

US President Barack Obama led international condemnation, saying it was "an attack on all of humanity", and New York lit the new World Trade Center in the red, white and blue of the French flag in sympathy.

Mr Obama is one of dozens of world leaders expected to attend key UN climate talks just outside the French capital from November 30.

Russian President Vladimir Putin said: "This tragedy has become another testimony of terrorism's barbarity, which poses a challenge to human civilization."

He called for concerted international efforts "against this evil".

Authorities had already tightened security at France's borders on Friday, hours ahead of the carnage in Paris, while European governments held emergency security meetings to respond to the crisis.

The attack is likely to complicate Europe's reaction to the thousands of migrants from Syria who have been fleeing the war to seek refuge in the 28-member bloc.

Last evening,The Guardian reported that Poland had already made a dramatic decision to stop taking refugees.