Story highlights Nine people are injured

Mudslide is likely cause of the train derailment

More than 200 people were on board

(CNN) A train car went off the rails and ended up in a creek in Northern California on Monday night, according to the Alameda County Fire Department.

The train derailment was likely caused by a mudslide, with a "pretty significant big" tree being a secondary cause, Union Pacific spokesman Francisco Castillo said. Nine people were hurt; four suffered injuries that were described as serious but not life-threatening.

Authorities earlier reported that 14 people had been injured.

"The train flipped over, and then I saw people, you know, falling over from the other side," passenger Jay Vijayen told CNN affiliate KGO. "The next thing we knew, we started seeing water coming into the bottom of the train. It was rising fast."

All the passengers from the derailed train have been removed, authorities said.