BEIJING - Seven people were killed and 59 injured in an explosion Thursday at the front gate of a kindergarten in eastern China as relatives were picking up their children at the end of the school day, local officials said.

The blast at the Chuangxin Kindergarten in Fengxian, which struck at 4:50 p.m., was under investigation, the Xuzhou city government in Jiangsu province said on its microblog.

It wasn't immediately clear whether the explosion was deliberately set or the result of an accident.

The official newspaper Global Times reported on its website that the incident was caused by the explosion of a gas cylinder at a roadside food stall, citing a witness identified only by the surname Shi. The blast sent people flying several meters (yards) into the air, Shi was quoted as saying.

Kindergartens in China have been targeted before in apparent revenge attacks carried out by mentally ill people or those bearing grudges against their neighbors and society.

Videos purportedly from the scene and posted on social media showed children and adults lying on the ground, some bleeding. Clothing, shoes and other items were strewn on the ground beside pools of blood. The videos showed ambulances arriving and medics wheeling people into an emergency room.

The Xuzhou government said two people died at the scene and five others died at a hospital. At least four others were seriously injured, it said.

Calls to the kindergarten and local hospitals rang unanswered.

In 2010, nearly 20 children were killed in attacks on schools, prompting a response from top government officials and leading many schools to beef up security with the posting of guards and the installation of gates and other barriers. Last year, a knife-wielding assailant injured seven students outside a primary school in a northern city.

China maintains tight control over firearms and most attacks are carried out using knives, axes or homemade explosives.