BBC: A lorry has struck a crowd after Bastille Day celebrations in the southern French city of Nice, killing at least 77 people and injuring dozens, officials say.
It happened on the famous Promenade des Anglais after a firework display. The driver was “neutralised”, and guns and grenades were found inside the lorry.
One image on Twitter showed about a dozen people lying on the street.
Officials said it was an attack, and asked people to stay indoors.
About 50 people were injured, some critically, in the incident on Thursday evening.
Nice Mayor Christian Estrosi said that “a lorry driver appears to have killed dozens of people”.
Prosecutor Jean-Michel Pretre said the lorry drove 2km (1.2 miles) through a large crowd, the AFP news agency reports.
The mayor and police urged residents to stay indoors.
Interior Ministry spokesman Pierre-Henry Brandet denied earlier reports of hostage situations and said the driver of the lorry had been “neutralised”.
He added that officials were investigating whether the driver acted alone.
No group has so far claimed responsibility, however prosecutors said the inquiry would be handled by anti-terror investigators.
French President Francois Hollande was returning back to Paris for crisis talks in the capital, his office said. Mr Hollande was in the southern city of Avignon on a private visit.
Meanwhile, Interior Minister Bernard Cazeneuve was on his way to Nice.
Some reports spoke of shots being exchanged between police and the occupants of the lorry but these have not been confirmed.
Social media video showed people running through the streets in panic following the incident.
A journalist with the Nice Matin newspaper reported from the scene that there was “a lot of blood and without doubt many injured”.
An AFP reporter said the incident took place as the firework display was ending, adding: “We saw people hit and bits of debris flying around.”
Another image on Twitter showed a white lorry stopped in the middle of the promenade with damage to its front, and four police officers observing it while taking cover behind a palm tree.
One eyewitness told BFM TV: “Everyone was calling run, run, run there’s an attack run, run, run. We heard some shots. We thought they were fireworks because it’s the 14th of July.
“There was great panic. We were running too because we didn’t want to stick around and we went into a hotel to get to safety.
Another witness, Roy Calley told the BBC that there were “thousands of people on the promenade” when the incident happened.
US President Barack Obama condemned “in the strongest terms what appears to be a horrific terrorist attack in Nice”, the White House said.
The president had been briefed about the situation “and his national security team will update him, as appropriate”, National Security Council spokesman Ned Price said.
France had already been on high alert, following last November’s attacks in Parisin which 130 people died and hundreds were wounded.
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