BOSTON — A gasoline tanker truck exploded into flames as it crashed early Saturday just north of Boston, setting off a fireball several feet high, killing the truck driver and injuring four other motorists, state police said.

Fuel from the truck spilled onto U.S. 1 near Saugus in the 2:30 a.m. crash and flowed into a drainage ditch before going up in flames. State police spokesman David Procopio said two greenhouse buildings and a private home caught fire in a secondary explosion.

Six other vehicles were damaged, and some went up in flames as the drivers tried to avoid the crash and fuel gushing from the overturned truck.

The driver of the truck, which belongs to PJ Murphy Transportation Inc. of Methuen, was killed. The company didn’t immediately return a call for comment.

For reasons that are unclear, the tanker slammed into a median, rolled over and exploded into flames, sparking a fireball, police said.