An accidental bonfire explosion at a town fair north of Paris injured 18 people, including three children, as the festive spring event turned into chaos, authorities have said.

Five of those injured, including one child, were taken to hospital with serious injuries but their lives are not in danger, said fire service spokeswoman Nathalie Crispin.

A few hundred people, including local families, the mayor and other officials, had gathered for the annual carnival in Villepinte and were getting ready to watch its climactic event - the lighting of a traditional bonfire, Ms Crispin said.

The fuel used to light the fire was apparently mishandled, however, prompting the explosion, she said.

Onlookers were hit by chunks of burning wood and suffered primarily from burns.
Ms Crispin and officials from the local police and the prosecutor's office of the Seine-Saint-Denis region said the explosion was found to be accidental.

France is in a state of emergency after Islamic extremist attacks in recent years but authorities said there were no signs of arson or terrorism in Saturday's explosion.