You have to pull over and stop for an emergency vehicle even if it is headed toward you in the opposite lane of a two-lane roadway.
Note well that an emergency vehicle which uses signals can be unpredictable and is allowed to legally violate traffic rules.
The driver can exceed the speed limit, pass red lights and STOP or YIELD signs, go the wrong way on one-way streets and turn in directions not normally allowed. Thus be cautious when an emergency vehicle heads toward you.