France has declared a state of emergency and people in Paris are being told to stay at home after at least 127 people were killed in six co-ordinated attacks across the capital.

A further 99 people are in a critical condition after the violence, which French President Francois Hollande has described as an "act of war" by Islamic State.

He said the murders were "committed by a terrorist army, the Islamic State group, a jihadist army, against France, against the values that we defend everywhere in the world".

He said France "will be merciless toward the barbarians of Islamic State group".

IS said the near-simultaneous attacks were a response to insults of the Prophet Muhammed and French airstrikes in IS territory.

The extremist group's statement warned the attacks were "only the start of the storm".

Mr Hollande vowed the country would "act by all means anywhere, inside or outside the country".

He also declared three days of national mourning and put the country's security on the highest level of alert.

In addition to the provisional death toll, 99 people are in a critical condition.

Earlier officials said at least 38 people died in shootings and bombings at bars, restaurants and a stadium in the capital - more than 80 are thought to have been killed at the Bataclan concert hall.

Eight attackers have been killed, the prosecutor said. Seven of them died in suicide blasts.

Security at venues across the city is being stepped up and police are hunting possible accomplices.

One Irish citizen was injured in the attacks.

President Hollande had earlier said France will be "merciless" against those behind the deadliest attacks in the country in decades.

Attack sites

A person is being evacuated after a shooting, outside the Bataclan theater in Paris. Image: Thibault Camus / AP/Press Association Images

The scene of the worst carnage was at the Bataclan music venue in the city's east.

Three gunmen took dozens of people hostage after first spraying cafes near the building with assault rifle.

At short time later, elite police commandos launched a dramatic assault on the theatre, but they were unable to save all the hostages.

Three attackers died at the popular music venue - two detonated explosives, while the third was killed in the police raid.

Around 1,000 people were believed to be at the venue to watch Eagles of Death Metal. The American band was later confirmed as safe.

North of the concert venue, a gunman killed at least 11 people at a Cambodian restaurant and a nearby bar in the 10th arrondissement - not far from the offices of Charlie Hebdo.

18 people sitting at outdoor terraces were also killed on the Boulevard de Charonne in the 11th arrondissement.

Another five people died on Rue de la Fontaine au Roi in the same district. The victims were reportedly at a pizza restaurant when they were killed.

Around the same time, three bombings, including two suicide attacks, occurred near the Stade de France stadium, where the national football team had been playing Germany in a friendly match.

Two of the blasts happened at entrances to the stadium and another at a nearby restaurant.

It has been reported that three people were killed there.

Mr Hollande was inside the stadium at the time, but rushed to the interior ministry to deal with the unfolding crisis.

Those at the stadium rushed on to the pitch after hearing the explosions.

Response

French soldiers and a police officer stand on a street next to Rue de Charonne, in Paris. Image: Thibault Camus / AP/Press Association Images

Amid the attacks, residents of Paris were asked to stay home and several Metro lines closed.

Around 1,500 soldiers have since been mobilised to protect official buildings, schools and universities.

Disneyland in Paris has remained shut for the day.

Mr Hollande earlier said the country's borders were being shut, but officials later clarified that they were just re-imposing border checks which had been removed after Europe created its free-travel zone in the 1980s.

He said the military was being deployed around the capital.

US President Barack Obama has described the attacks as an "outrageous attempt to terrorise civilians" and has promised to do everything he can to bring those responsible to justice.

"Those who think that they can terrorise the people of France or the values that they stand for are wrong".

The New York Police Department said it had bolstered security at high-profile locations in response.

In an updated travel notice, the Department of Foreign Affairs is urging Irish people in France to follow the instructions of authorities there.

France has been on edge since deadly attacks by Islamic extremists in January on satirical newspaper Charlie Hebdo and a kosher grocery store that left 20 dead, including the three attackers.