Four people were killed and 11 others injured in an explosion at a residential building on Friday morning in northeast China's Liaoning province, Xinhua news agency reported.Part of the building collapsed after the blast at around 5 a.m. in Huludao city, according to a statement from the city publicity office.The last survivor was rescued 12 hours after being trapped in the debris and the body of the last missing was retrieved two more hours later.The 11 injured, including residents and passersby, have been sent to hospital."I thought it was an earthquake," said a resident who was caught in the blast. "I rushed out of the building immediately, and found smoke blowing out from the building."The explosion was thought to have been caused by a gas leak.A similar explosion in Huludao city on May 31 left two people dead and 11 injured.