UPDATE: The Alameda County Sheriff's Office announced Thursday that Deputy Mike Foley died from his injuries.

Original Story:

An Alameda County sheriff’s deputy was in “touch and go” condition Wednesday after an inmate transport bus struck him at Santa Rita Jail in Dublin, officials said.

Deputy Mike Foley, who is about 60, was struck by a bus driven by another sheriff’s deputy in the jail parking lot at about 6 a.m., said Alameda County Sheriff Gregory Ahern.

The driver of the bus was going about 15 mph and didn’t see Foley, who was wearing dark clothes, in the morning darkness until it was too late, Ahern said.

“This is just an accident,” Ahern said, adding that the California Highway Patrol is investigating the incident.

The deputy was in “extremely serious” condition at John Muir Medical Center in Walnut Creek, said Sgt. Ray Kelly, spokesman for the sheriff’s office.

Foley was initially taken to the closest hospital to the jail, Eden Medical Center in Castro Valley, but was moved to John Muir because of the severity of his injuries. His son, who attends college in Southern California, was flying to the Bay Area on Wednesday afternoon to be at his father’s side, Ahern said.

Foley underwent surgery Wednesday to relieve swelling on his brain caused by extensive head trauma, Ahern said.

Foley joined the Alameda County Sheriff’s Office in 2007, after serving for 30 years as an officer with the Concord Police Department. He was a member of the sheriff’s office transportation unit, which handles inmate transit.

No inmates were aboard the bus that hit Foley, Ahern said. The driver and another deputy were leaving the jail to pick up lunches for inmates when the incident occurred. As part of protocol, the driver, whose name was not released, was placed on paid administrative leave.

Ahern said that while Foley is the oldest member of the transportation unit, he is the “hardest working.” As usual, Foley showed up an hour early Wednesday, intending to begin an overtime shift at 7 a.m.

Dozens of officers from all over, including the Contra Costa County Sheriff’s Office, the Concord Police Department, the Walnut Creek Police Department and the California Highway Patrol, converged at the hospital to show support for Foley.

Michael Bodley is a San Francisco Chronicle staff writer. Email: mbodley@sfchronicle.com Twitter: @michael_bodley