There's an approaching emergency vehicle using its flashing lights and siren. You should:

You must yield the right-of-way to police vehicles, fire engines, ambulances, or other emergency vehicles using sirens, air horns, or red or blue flashing lights. When you see or hear an emergency vehicle approaching from any direction, you must pull over to the right edge of the road, or as near to the right edge as possible, and stop your vehicle.
DMV Writen Test