Two fire trucks answering a call collided at an intersection in a Los Angeles suburb Wednesday, sending one careening into a restaurant and leaving 15 people injured, including six firefighters.

One of the victims was in critical condition, authorities said. Three or four suffered minor to moderate injuries and there were nearly a dozen "walking wounded," reported.

The crash left one truck embedded in a Chinese restaurant, with rubble scattered across the sidewalk.

"There was a loud boom and a lot of shaking. I thought it was an earthquake," said Wendy Wu, a waitress who was in a walk-in freezer when the truck plowed through the front of the restaurant.

When she walked out from the freezer, uninjured, she saw a refrigerator pushed across the room and furniture in disarray. Wearing a uniform with the restaurant logo and speaking through an interpreter, she said she saw several injured people bleeding and attempting to stand.

Monterey Park Fire Chief Jim Birrell told reporters that trucks from his city and neighboring Alhambra were responding to a house fire shortly after 3 p.m. when they slammed into each other at an intersection. One truck then plowed into the restaurant.

An investigation is underway to determine what caused the crash.

Birrell said at least 14 people were injured, one critically. Rosa Saca, a spokeswoman for Los Angeles County-USC Medical Center, said nine victims were brought there, including the five firefighters. She said the critically injured person was among the hospital's patients but is not one of the firefighters.

Monterey Park is about 15 miles east of downtown Los Angeles.

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The Associated Press contributed to this report.