An explosion at a 676-room Mexican resort killed as many as seven people and injured at least 20 more on Sunday. Four Canadian citizens were killed in the blast, officials in Canada have confirmed, including a nine-year-old boy. And two Americans were injured, according to the U.S. State Department. An additional two casualties were thought to be hotel employees. Images of the resort, the Grand Riviera Princess hotel in Playa del Carmen, show glass shards and debris scattered among its dozen buildings. The explosion is thought to have been caused by natural gas from a local swamp that accumulated underneath the hotel and was ignited.