A section of a building being demolished in Philadelphia has collapsed onto a street, coming to rest against a school bus but causing no injuries.

The fallen slab of concrete also knocked a small tree and light pole onto the bus.

Bus driver Spencer Reynolds says he'd just dropped off a group of elementary school students at the National Constitution Center on Thursday morning when the collapse happened nearby.

He says he was stuck in traffic when he heard rumbling. He says windows were shattered, and glass and debris were thrown into the bus seats.

Most of the building slab fell on a section of street blocked off by barriers.

In 2013, six people were killed when a building under demolition in the city collapsed on a neighboring thrift store.