Investigators say a mudslide most likely caused a commuter train to derail in a remote area of Northern California late Monday, sending one of the leading cars tumbling into a swollen creek and injuring nine people.

The apparent mudslide swept a tree onto the tracks, derailing a car on the Altamont Corridor Express train, Union Pacific Spokesman Francisco J. Castillo said.

Fire officials said four people were seriously hurt, while five others had minor injuries.

"It was dark, wet, it was raining. It was very chaotic," Alameda County Sheriff's Sgt. Ray Kelly said. "This is an absolute miracle that no one was killed, no passengers or first responders."

Alameda County Sheriff's Department spokesman Sgt. J.D. Nelson told the Associated Press that the two front cars on the Altamont Corridor Express (ACE) train No. 10 went off the tracks near Niles Canyon Road in Sunol, about 45 miles east of San Francisco.

Images posted on Twitter showed one of the cars partially submerged in water.

Nelson said crews had to fight the creek's currents to pull riders from the partially submerged rail car.

Altamont Corridor Express official Steve Walker said the train's first car was carrying six passengers and one crew member when it fell into Alameda Creek. He said the second car also went off the tracks, but remained upright.

There were 214 passengers traveling in the train at the time of the derailment, officials told KCBS. The uninjured riders were transported to the Alameda County Fair in Pleasanton after being checked by paramedics.

According to the ACE's website, the train departed San Jose at 6:38 p.m. local time and was due to arrive in Stockton at 8:50 p.m. local time. The operator announced that no trains will run on Tuesday.

The Associated Press contributed to this report.

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