SAN FRANCISCO, Nov. 28 (Xinhua) -- An engine fire prompted a United Airlines flight return to San Francisco International Airport (SFO) on Monday afternoon.

SFO spokesman Doug Yakel said UA flight 837 "experienced some kind of engine issue and had to shut down one of its four engines" shortly after taking off from the airport for Tokyo, Japan, on 11:36 a.m. local time.

Witnesses reportedly heard the sound of an explosion and saw flames emanating from one of the Boeing 747's engines on the left side, and the plane then circled above the airport for more than an hour before returning safely to the ground.

No injuries were reported among 202 passengers and 15 crew members on board the plane.