A car mowed down a group of performers preparing for a carnival parade in southern Belgium early Sunday, killing six people and leaving 10 more with life-threatening injuries, officials said.

More than 150 people had gathered at dawn with costumes and drums for the festival in Strépy-Bracquegnies when suddenly, “a car drove from the back at high speed,” said Jacques Gobert, mayor of the neighboring town of La Louviere.

In addition to those killed and the 10 who were critically injured, several dozen suffered minor injuries, authorities said.

The driver and a second person were arrested after the car was stopped a few miles away. The duo, who are both in their 30s, had not been previously known to police.

It’s unclear what caused the deadly incident.

But prosecutor Damien Verheyen said, “there is no element in the investigation at this time that allows me to consider that the motivations of the two could have been terror related.”

Belgian Interior Minister Annelies Verlinden expressed grief over the incident.

“What should have been a great party turned into a tragedy,” Verlinden said.

With Post wires