Huge fire damages apartment complex in US

A massive fire has caused catastrophic damage to a apartment building complex in San Francisco's Mission Bay district.

A huge, out-of-control fire has caused catastrophic damage to a quarter-billion-dollar apartment complex under construction in San Francisco.

The massive blaze broke out shortly after 5pm on Tuesday (1100 AEDT Wednesday), spreading through the building quickly and sending embers floating toward nearby buildings as fire crews worked to contain the blaze.

Shortly before 6pm, one side of the building collapsed, and a fire dispatcher with the department confirmed the structure was collapsing internally.

"Everybody is heading there," the dispatcher said. "We don't go past five alarms in this city."

The fire appeared to totally destroy MB360, a $US227 million ($A253.62 million) apartment complex being developed by San Francisco-based BRE Properties Inc at Fourth Street near China Basin. The project was slated to open sometime later this year.

Representatives for the development company were not available for comment.

There were no reports of injuries as of 7pm. Fire crews pulled back from the building around 6pm to stay clear of possibly spreading flames or collapsing walls.