A blast outside a kindergarten in a county north of Shanghai killed at least seven people and injured 66 others yesterday, said the authorities.

The explosion went off at 4.50pm, when parents and grandparents were waiting for their young charges outside Chuangxin Kindergarten in Fengxian, in the eastern coastal province of Jiangsu.

Photos and videos circulating online showed several adults and children lying on the ground, some covered in blood and with their clothes torn off by the force of the blast.

One video showed a man covered in blood trying to stand up before he stumbled; another had people screaming and shouting for help. Some of the online videos were deleted after a few hours.

According to the local authorities, as of 7.45pm last night, two people had died instantly at the site of the blast, while five died in hospital.

At least 66 others were hurt, including nine who had sustained serious injuries.

The local police said the cause of the explosion was still under investigation, while state media described the blast as an accident.

The local authorities said no children or teachers from the kindergarten were hurt in the incident as they were still having lessons when the explosion took place.

Chinese online media reported that a shop owner near the kindergarten had heard a loud "bang" at around 5pm. He later found out that an explosion had happened at the entrance of the kindergarten just 100m away.

The Global Times and China Youth Daily newspapers cited witnesses as saying that a gas cylinder at a food stall had exploded. Some netizens on China's Twitter-like Weibo service questioned the use of gas canisters by street food stalls, noting that these posed a danger.

Yesterday's blast was the latest tragedy at a kindergarten in China in recent weeks. Last month, a school bus with pre-schoolers on board caught fire inside a tunnel in eastern Shandong province. All 11 children, a teacher and the driver died inside the bus. The authorities later announced that the driver had set the bus on fire as he was angry at losing overtime wages.

There also had been instances of mass stabbings in schools in various parts of China in recent years.

In January, a middle-aged man attacked and wounded 11 children with a kitchen knife at a kindergarten in Guangxi Zhuang autonomous region in the south.

From 2010 to 2012, a series of stabbings, cleaver and hammer attacks took place in schools across China, leaving at least 25 people dead and some 115 injured.