If an emergency vehicle with red flashing lights or using a siren is moving in your lane, you are required to

Authorized emergency vehicles, such as police cars, ambulances, and fire engines, have the right-of-way when they are signaling audibly (siren) or visually (flashing lights). When you hear or see a vehicle approaching, you should immediately pull over to the curb, stop, and remain stopped until the emergency vehicle has passed. [Emergency Vehicles; Sharing the Road; California Driver Handbook]