Terrorist gunmen and bombers have brought horror to Paris with as many as 100 feared killed, dozens injured and up to 100 taken hostage in multiple shootings, suicide attacks and bombings across the city.

Some of the shootings, by men with Kalashnikovs, took place near the Charlie Hebdo office. Explosions took place just outside the soccer stadium, Stade de France, where France was playing a friendly martch against Germany.

British Prime Minister David Cameron expressed his shock and said: "We will do whatever we can to help." US President Obama described it as "an attack on all of humanity."

The Archbishop of Canterbury Justin Welby said: "Tragic Paris, desperate news of deep tragedy, with heartbreak for so many. We weep for those affected, pray for deliverance and justice."

The President of France François Hollande, who was among spectators at the Stade de France when two suicide attacks and one bombing hit, declared a state of emergency, closed borders and mobilised 200 troops across the city. He described the events as "horrifying" and said France was witnessing events of an "unprecedented magnitude". There were reports of a dismembered body at the stadium, giving adding weight to theories that it was a jihad-inspired terror attack.

Witnesses described stepping over dead bodies near a restaurant that was the scene of one of the attacks. There are thought to have been at least seven attacks in total.

Many were shot and killed at the Bataclan concert hall, where a heavy metal band were playing. U2 were due to play a concert in Paris on Saturday night. 

There were at least five explosions and further shootings outside the concert hall where the hostages were being held, with growing fears for the safety of the hostages and concerns that they too were in deadly danger.

One of the many attacks was at Le Petit Cambodge restaurant in the Eleventh district of Paris. A BBC reporter described seeing 10 people lying on the road, dead or seriously injured. As international media descended on the affected areas, the horror continued to unfold, television stations capturing footage of attacks, and of the police and security force responses as they took place.

Security forces launched an assault on the concert hall where the hostages were being held as the situation continued to unfold. Acting on intelligence that people were being killed inside the concert hall, police and troops went in and shot and killed the two terrorists, bringing that particular incident to a close. One police official said it was "carnage" inside the building, with the terrorists tossing explosives at the hostages and murdering as many as possible in as short a time as possible. It seems there could have been up to 100 casualties in the theatre attack alone. It is thought that this is what prompted the rapid assault from the security services, who will have had to use explosives themselves to get through the many doors in one of Paris's oldest and best-loved theatres.

Parisians used Twitter to reach out to people in need of shelter and taxi drivers turned off their meters to take people home for free. A British emergency number for people wanting news of loved ones in Paris has been published: 020 7008 1500.