Between nine and 15 suspects attacked the 47-year-old man at about 7:30 p.m. during a strong-arm robbery at the station, located at 1 James Ave., spokeswoman Christine Dunn said.
The suspects fled before San Mateo County transit police arrived, but investigators are following up on potential leads from witnesses.
The victim was taken to a hospital and was listed in critical condition as of today, Dunn said.
She was not able to discuss the nature of the victim's injuries or details of the investigation, but said police are asking for the public's help in the case.
"This is a particularly violent assault. It's something we want to resolve as quickly as possible," Dunn said.
Anyone with information about the attack is asked to call transit police Detective Victor Lopez at (650) 622-8048.