At least 12 people were killed in Chicago, Illinois, when a crowded third floor porch collapsed during a party.

Authorities say 45 others were injured in the accident, some of them critically.

Police say as many as 50 people - most of them in their early 20s - were on the wooden porch when it collapsed early Sunday, crushing the first and second floor porches below.

Medical officials say most of the dead appeared to have been standing on the lower story porches at the time of the accident.

Officials say they do not know what caused the porch to collapse, but say it could be because of overcrowding.