LOUISVILLE, N.Y.—Federal and state authorities are investigating a crash involving a small bus and box truck in snowy conditions that killed six people in upstate New York near the Canadian border.

The accident happened around 6 a.m. Saturday on Highway 37 in Louisville, about 150 miles north of Syracuse along the St. Lawrence River.

State police said the six people who died, as well as three others who were seriously hurt, were on the bus. One of the people injured was in critical condition.

The bus had the logo of a solar energy company, LBFNY, WWNY-TV reported.

Matt Denner, emergency services director for St. Lawrence County, told WWNY that numerous ambulance crews and other first responders were at the scene.

“It was a very difficult scene for everyone there,” Denner said.

State police and the National Transportation Safety Board (NTSB) are investigating the cause of the crash. The NTSB said it launched a six-member team to perform a safety investigation.