A Canadian eyewitness who was at the Bastille Day celebrations in Nice, France, moments before a truck plowed into a crowd of people killing dozens, says the crowd was packed with families with young children.

"This was a family event, there were babies, there were children, and just watching these people dragging their children down the street was unbelievable, and we're running with them," said Ramiro Mora, a consultant from Toronto vacationing in Nice. "It was just absolute chaos."

'This was a family event, there were babies, there were children,' says Ramiro Mora, a consultant from Toronto vacationing in Nice. (@ramiro_H_Mora)

Mora was on the Promenade des Anglais watching the Bastille Day fireworks display with what he said were tens of thousands of other spectators. After the show was over he began making his way back to his apartment when the truck hit the crowd.

"I just heard people yelling and I turned back and there were hundreds of people running up the street and I looked over at another street and hundreds, thousands, of people running again there too," he said.

Mora said local media in Nice are instructing people there to stay in their homes and hotels and not to venture out onto the streets.

​Prime Minister Justin Trudeau took to Twitter to offer his sympathy. "Canadians are shocked by tonight's attack in Nice. Our sympathy is with the victims, and our solidarity with the French people," he said.

Canadians are shocked by tonight's attack in Nice. Our sympathy is with the victims, and our solidarity with the French people. —@JustinTrudeau

In a further statement Trudeau said, "Canada and France are the closest of friends, and we stand by the French people as they face this terrible ordeal. We have offered all possible assistance to the French Government.

"Senseless acts like this one are not isolated events, and we will continue to work with our Allies and partners to fight terrorism in all of its forms. We will bring those who are responsible to justice, whether they be the perpetrators, or those involved in funding or organizing such attacks."

Global Affairs Canada has updated its travel advice for Canadians going to France, saying that people should "exercise a high degree of caution."

"There is no nationwide advisory in effect for France," the government's website said. "However, you should exercise a high degree of caution due to the current elevated threat of terrorism."

Contact information for Canadian consular services in France: <a href="https://t.co/oyLW3pqzRp">https://t.co/oyLW3pqzRp</a> —@TravelGoC

Among the Canadians vacationing near Nice was Marc Roy, who abandoned his usual motorhome vacation to take his family to the south of France.

Roy, who works as director of communications to Transport Minister Marc Garneau, reassured friends on Facebook that they were OK.

"For all of those sending messages, please know that we are safe and sound following this evening's event in Nice, France," he wrote around 6 p.m. Thursday.

"We decided not to go see the fireworks on La Promenade des Anglais which is merely 15 minutes from our house."

It remains unclear if any Canadians have been injured or killed in the attack.