An explosion rocked the Westchester area today, killing a Los Angeles firefighter and critically injuring another.

The firefighters were called to Sepulveda and La Tijera boulevards at 1:57 p.m. after a report of smoke from a possible fire. After they arrived, there was a larger explosion that sent several manhole covers flying, said Ron Myers, spokesman for the Los Angeles Fire Department. Initial reports attributed the death and the injury to the projectiles, but authorities now believe the blast inside the building may have been to blame. A rescue helicopter was called in to transport the injured individuals to a nearby hospital, Myers said.

The names of the firefighters have not been released, Myers said.

A source close to the investigation told The Times that the blast was so powerful it sent one of the firefighters through a wall and into a parking lot. The investigation into the bast is focusing on a possible electrical malfunction, the source said.

The blast also significantly damaged a bank building on Sepulveda Boulevard.

Deputy Fire Chief Mario Rueda said the firefighters were investigating a report of smoke and entering the building when the final explosion occurred.

"They were making entry into a metal clad door" on an electrical equipment room, he said.

Stucco and other materials flew out, hitting a nearby fire engine, Rueda said.

Optometrist Kent Ashcraft, who was working in a nearby office, said he heard two blasts. The second was "like a sonic boom. The walls shook," he said.

Cheryl Jackson, an optician who works with Ashcraft, said she heard three explosions. "I had never heard anything that loud," she said of the final blast.

"It's a sad day in Los Angeles. We lost a firefighter," said Mayor Antonio Villaraigosa.

bob.pool@latimes.com

molly.hennessy-fiske@latimes.com