This is the most urgent warning light because it means that your coolant and thus your engine is overheating. Stop in a safe area and let the engine cool down. Check for leaks in the coolant system, then check the coolant level, fans, and radiator cap.
Hyundai Elantra Red Warning Light? What function is the Red Warning Light for in the Elantra. This light flashes continuosly in my sister's car, so obviously there is a fault.