At least seven people were killed and 59 people were injured in an explosion at the entrance to a kindergarten in eastern China Thursday, city officials said.

The explosion occurred at approximately 4:50 PM local time, police said. The cause of the explosion is under investigation.

Unidentified witnesses told local newspaper Xiandaikuaibao that they had scene a bomb before the explosion. The witnesses said that the explosive was a bottle of cooking gas. The presence of a bomb has not been confirmed. The authorities do not know if the blast was intentional or accidental.

It is unknown how many children are among the dead and injured. The explosion occurred just as parents were arriving to pick their children up from school.