At least 20 families are feared trapped in the debris of a two-storey building that collapsed in Thakurli town in Thane district late Tuesday, officials said.The incident occurred around 10.15 p.m. when the tenement, Matrukrupa, in Cholegaon area of the town suddenly collapsed.Ten people were rescued from the debris of the three-decade old building.Eight fire engines have been rushed to the spot.Heavy rains hampered relief and rescue efforts and top police and civilian officials were present on the spot.