US President Donald Trump says he has been fully briefed on earthquake in Southern California. (File)

US President Donald Trump said Thursday that the situation in Southern California after a strong 6.4-magnitude earthquake appeared to be under control amid reports of scattered damage.

"Been fully briefed on earthquake in Southern California. All seems to be very much under control!" Trump tweeted.

The quake struck near the city of Ridgecrest and the US Navy's China Lake weapons testing range.

A hospital damaged by the quake in Ridgecrest was being evacuated, and an official at China Lake said there was "substantial damage" to their facilities, including fires, water leaks and spills of hazardous materials.