Four people were killed and another four were injured Saturday when an apartment building collapsed in southwestern Poland. Two other people were reported missing after the incident in the town of Swiebodzice, authorities said. Rescue workers searching for survivors described a grim scene, with two of those killed said to be children. Firefighters digging through the rubble in search of two more people thought to have been inside said they heard no sounds coming from the debris Saturday. Daniel Mucha, a regional spokesman for the firefighters, said two of the building’s three floors had collapsed, and it may have been caused by a gas explosion, the Associated Press reported. The pre-World War II building was recently renovated and thought to be in good condition, the local governor said. Regional authorities said the rescue operation will likely last through Sunday.