A pre-dawn explosion blew apart a five-story apartment building Thursday, killing at least four people, injuring seven and possibly burying others in the wreckage, officials said.

About 170 rescue workers aided by dogs searched the ruins for other survivors or victims. Dozens of emergency vehicles converged on the site.Police said 49 people lived in the building, in the town of Massy, on the western outskirts of Paris. By midmorning, all but eight to 10 residents were accounted for.

The cause of the early morning blast was not established officially, but firemen said it appeared to have been a gas leak.