Three people are dead and 18 are missing after three buildings in Rio de Janeiro, Brazil collapsed on Thursday at nine p.m. local time.

The buildings were 20 stories, 10 stories and four stories high. Six other people were also injured when the buildings came down.

Local police said they didn’t find any traces of a bomb or gas explosion. They said considering construction work that was taking place at the time of the accident the buildings could have collapsed due to structural defects.