Updated

A mother and her son, both firefighters, were in the "mop up" phase of putting out a vehicle fire along a busy interstate when semitrailer slammed into their fire truck early Wednesday, killing the son and injuring his mother, police said.

Jonathan French, 25, was killed and his mother, Lisa French, was taken to a hospital where she was in serious condition, Kentucky State Police Trooper Jeff Gregory said.

Firefighting ran in the French family. Jonathan French had volunteered for the Glendale Fire Department for about five years. Lisa French had been there for about seven years. Her brother is the agency's fire chief.

"It hurts us all because we are a brotherhood. The Glendale Fire Department is immensely devastated at this time," said Elizabethtown Fire Chief Michael Hulsey, whose department is nearby.

The crash occurred in central Kentucky along Interstate 65 about 3:30 a.m. Wednesday, about 1 mile north of Glendale, a town located 50 miles south of Louisville. The mother and son were getting equipment off the fire truck when it was hit.

"The semi struck both of them and also clipped the front end of the fire engine," Gregory said.

Gregory said the fire truck's emergency lights were on at the time of the crash. He didn't know the identity of the man driving the semi or what company he worked for.

Gregory also didn't know how many people were in the burning vehicle or if they were hurt. No charges have been filed.

The Glendale Fire Department has about two dozen firefighters.