Mumbai: Five persons were killed when their speeding car rammed into a tree on the Western Express Highway here on Thursday, an official said. The accident occurred at 5.45 a.m. opposite the western end of the Mumbai airport's main runway near the Milan Flyover, the official said. The impact of the crash was so grave that the Honda City car climbed up around 10 feet on the roadside tree before sliding off and killing four occupants on the spot, said an official. The investigators suspect over speeding as a probable cause, however, they have not ruled out the possibility of drunken driving or carelessness of driver as the highway is relatively traffic free during the early hours of the day. The victims aged between 19 to 25-year-old are yet to be identified.