Mexican authorities say a tanker carrying 25 tons of ammonia has crashed into a passenger bus in northwestern Mexico, leaving at least 38 people dead.

Investigators said Wednesday that the bus driver was among those killed in Tuesday's accident on a highway near Los Mochis in Sinaloa state. They say the crash caused a pipe on the tanker to break, triggering the release of much of the ammonia. Officials say a three-kilometer radius was affected by the toxic spill.

Authorities evacuated area residents as a precaution and closed the highway for several hours in order to seal off the area. One Mexican media report indicates speed may have been a factor in the crash, which caused the passenger bus to flip onto its roof.

Some information for this report provided by AP.