Six explosions boomed across central Baghdad on Sunday, sending plumes of smoke into the air and injuring at least 11 people, a hospital official said. Four explosions in a row hit the city Sunday evening. Several minutes later two more blasts shook downtown, and the crack of gunfire rang out. At least 11 people were taken to al-Kindi hospital with injuries, three of them in serious condition, said Mohammed Eidan, a health worker there. Some of them were injured when a blast hit a truck as it drove through downtown Baghdad, badly damaging the vehicle and collapsing part of a wall of a nearby house. Flames and smoke lept from the destroyed truck as firefighters tried to put out the blaze, and blood stained the street. Shrapnel also smashed the windows of a nearby car, the seat of which was covered in blood. In another district, rescue workers said two mortar rounds hit a police club where some men were playing soccer. One player and another man were injured in the blasts. Another of the blasts hit a bank of the Tigris River bordering the Green Zone, the fortified enclave housing the Iraqi government's offices and the U.S. Embassy. After the second set of explosions, an air raid siren sounded in the Green Zone.