Two people are in critical condition after a house exploded in St. Louis Thursday, authorities said. The cause of the blast on Thrush Avenue shortly after 10 p.m. local time (11 p.m. ET) has not been determined, but natural gas was cut off to the home, which was leveled by the explosion and caught fire, a spokesman for the St. Louis Fire Department said.Two men were trapped in the wreckage but freed by firefighters, the fire department said. They were taken to an area hospital and were in critical condition, but stable late Thursday.