By ANDREW SELSKY for the Associated Press

SALEM, Ore. (AP) — Firefighters responding to a fire at a barn in rural Oregon early Thursday were hit by an explosion, killing one of them, and investigators haven’t yet determined the cause.

Some 12 hours after the predawn blast it was still too dangerous for investigators to approach, Sgt. Jeremy Landers of the sheriff’s office said.

The blast occurred soon after firefighters arrived at the burning barn near the tiny town of St. Paul, located about 30 miles (48 kilometers) southwest of Portland. The fire was reported to authorities around 4 a.m.

The explosion critically injured volunteer firefighter Austin Smith. Paramedics already at the scene provided first aid and Smith was flown by a medical evacuation helicopter to Oregon Health & Science University Hospital in Portland, but he did not survive, Chief Bryan Lee of the St. Paul Rural Fire Protection District told reporters.

Smith, 30, of St. Paul, had been with the St. Paul Fire District since 2015.

“We in the community are absolutely heartbroken over this loss,” Lee said.

St. Paul has barely 400 residents, but hosts a rodeo every summer that attracts thousands of spectators. One of Smith’s relatives, Bill Smith, was the first president of the rodeo, first held in 1936. Lee spoke with reporters on the rodeo grounds.

Landers said it may be several days before information about the cause of the fire and explosion are released.

A farm that raises turkeys is located on the same gravel road where the barn was located, but it was unclear if the farm owned the barn. No one picked up the phone at Champoeg Farm or responded to a message.