"A fraction of a second later, an enormous white truck came along at a insane speed, turning the wheel to mow down the maximum number of people", he said.
An eye witness told i-Tele: "We nearly died".
Facebook on Friday turned on its Safety Check feature after a large truck mowed through a crowd celebrating Bastille Day in Nice, France, killing at least 80 people.
Police shot the driver dead after he drove the truck two kilometres (1.3 miles) through a crowd along the palm-lined Promenade des Anglais. "A truck drove into the crowd during fireworks".
Police shot and killed the driver, said Pierre-Henry Brandet, a spokesman for the French Interior Ministry.
A lorry hit crowds who had gathered to celebrate the French national day in the Mediterranean city on Thursday night.
A photo on social media showed a truck with what appeared to be bullet holes in its windscreen.
Nice prosecutor Jean-Michel Prette said bodies were strewn along the road. "You can see wreckage all along the way, a body, bicycles, street lamps and debris everywhere", he said.
"More info to come", Christian Estrosi, president of the Nice Cote d'Azur region, said in a translated tweet.
The French daily Le Figaro quoted security sources as saying, "several weapons, guns and grenades were found inside the truck".
In a Twitter message President Sirisena said he is appalled by the "cowardly nature" of the attack in Nice and offered condolences to the French state.
"The Los Angeles County Sheriff's Department employs thousands of uniformed deputy sheriffs who are on-duty 24 hours a day, seven days a week, patrolling and protecting the many diverse and varying communities we serve ...", officials said.
Hollande called a defense council meeting Friday with key ministers, and will head to Nice after that. "It's all of France which is under the threat of Islamic terrorism", he said.
France has been under emergence since the attacks in Paris previous year.
It was not immediately clear who would have been behind an attack, but France has recently seen a spate of dramatic assaults from by jihadist groups, including the Islamic State group which straddles Iraq and Syria.
Nice, a metropolitan city of about 340,000, is located in southeast France on the Mediterranean Sea. A jazz festival due to begin Saturday and a Rihanna concert planned for Friday have been cancelled.
Who was the truck driver?
"There was a lot of screams coming from ahead of us where the truck was ..."
Police and ambulances went to the scene and authorities from the local Alpes-Maritimes prefecture urged residents to stay indoors.
France's Terror Prosecutor's Office has officially opened an investigation into the incident.
The tournament brought an all-too-brief burst of joy to a gloomy France, bogged down after the two attacks in 2015, violent anti-government protests, strikes and floods.
"Once again innocent people have been targeted at an occasion of joy and celebration".