A man's legs have been crushed by a 500-kilogram concrete slab that fell at a Brisbane home.

A delivery worker heard someone yelling for help on Soden Street in the southside suburb of Yeerongpilly about 9.20am on Friday and called triple-zero.

The man, described by paramedics as elderly, suffered serious leg injuries.

He was taken to the Princess Alexandra Hospital in a stable condition just after 10am.