Three people were killed and six others remain missing after a residential building collapsed in a methane gas explosion in Italy's Sicilian town of Ravanusa, the National Fire Corps have tweeted.Two people have been so far pulled from the rubble alive, the Fire Corps said on Sunday, while 50 families have been evacuated from surrounding buildings, according to RAI News 24 public broadcaster.The explosion that occured on Saturday night has destroyed three buildings, the ANSA news agency reported.Agrigento Fire Brigade Commander Giuseppe Merendino told ANSA the gas had accumulated either underground or in a closed environment, Xinhua news agency reported."The leak could have been caused by landslides or adverse weather," he added.