An explosion on Thursday struck a kindergarten in eastern China when children were leaving the school, resulting in several casualties, the state media reported.

The blast happened at 4:50 p.m. at the gate of the kindergarten in Fengxian County in east China’s Jiangsu Province, officials were quoted as saying by the state-run Xinhua news agency.

Police said they are investigating and have no word yet on injuries or deaths.

Witnesses said there were casualties, but the exact number was unclear, the report said.

According to Hong Kong based South China Morning Post, dozens of people were reported to have been injured in the explosion.

It was not immediately clear what caused the blast.

Pictures and videos posted online showed at least a dozen people lying outside the gate of the kindergarten, the paper said.

Some victims were seen covered in blood while others appeared to be unconscious and some even with their clothes burned off. Children were seen among the injured.

“About 5 pm, we heard a blast and thought it might have been a gas explosion at a nearby food vendor,” a local shopowner was quoted as saying by online news portal Sohu.

“Many people could be dead,” he said.

In one video clip posted online, a man covered in blood was seen trying to stand up only to collapse again. His clothes appeared to have been burned off.

In a separate video clip, people could be heard shouting: “Blast, blast, dial 110 quickly!”

The gate of the kindergarten appeared to have been horribly bent, with shattered glass littering the scene.

China in the past witnessed knife attacks on kindergarten children by disgruntled people. An explosion of this magnitude was rare.