Emergency crews are on the scene of a bridge collapse in Pittsburgh.

Police reported the span, on Forbes Avenue over Fern Hollow Creek in Frick Park, came down at around 6am.

A photo from the scene shows a bus upright on a section of the collapsed bridge.

There were no initial reports of injuries, Pittsburgh Public Safety said on Twitter.

A natural gas line was cut and there is a smell of gas in the air, the agency said.

Authorities told motorists to avoid the area.

The collapse came hours before President Joe Biden visits the city to talk about his trillion-dollar infrastructure bill that includes bridge maintenance.