Six people died and seventy were injured from a Metro trains' collision in Washington D.C., on Monday during rush-hour, but the cause of the accident still unknown.

The incident killed at least six people and injured scores, Mayor Adrian Fenty said today, according to CNN. 56 people showed minor injuries, 12 had moderate injuries and two were critically injured, Chief Dennis Rubin of Washington's Fire and Emergency Medical Services Department told the news agency.

Both trains were in the same track. The cause won't likely be known until several days after as the investigation unfolds. Officials said one train hit another train that was still.

It was the deadliest crash in the 33-year history of the city's Metro train subway system, Mayor Fenty said.

The incident happened in the Red Line just before 5:00 p.m. EDT between Fort Totten and Takoma stations.