BEIJING - Eleven South Korean and Chinese kindergarteners and their driver were killed when a school bus crashed and burst into flames in a tunnel in eastern China on Tuesday, officials said.

The children were aged between three and six and attended a South Korean international school in the city of Weihai, Shandong province, local authorities said. A teacher was seriously injured in the tragedy, which reverberated in South Korea, whose acting president expressed sorrow.

The Weihai propaganda department said five of the young victims were South Korean and six were Chinese.

But a South Korean consular official in the eastern city of Qingdao told AFP that 10 of the children were South Korean, though five of them were dual Chinese nationals. The official also said the children were aged four to seven.

Weihai authorities said the children were on their way to the Weihai Zhongshi South Korean International School when the accident occurred at the Taojiakuang tunnel at around 9:00 am.

An amateur video posted by the People's Daily on its Twitter account shows cars driving away from the bus, which was stopped near a wall as flames reached the tunnel's ceiling. The video's authenticity could not be immediately verified.

The cause of the crash was under investigation.

South Korea's Acting President Hwang Kyo-Ahn voiced "grave sadness" over the tragedy, which occurred as the country went to the polls to elect a new president.

Hwang told the foreign ministry to mobilise "all diplomatic resources" to handle the accident and keep the parents of the young victims informed of any developments.

Deadly road accidents are common in China, where traffic regulations are often flouted or go unenforced by police.

There were more than 180,000 traffic accidents and 58,000 deaths in 2015, authorities said in December.

The country's frequently overcrowded long-distance buses are particularly prone to high fatalities.

Ten people were killed and 38 injured in March when a bus collided with a cement truck in the southwestern province of Yunnan.

At least 18 people were killed when a minibus plunged into a lake in the central city of Wuhan in December.

Last November, a pile-up on an expressway in the northern province of Shanxi killed 17 people and damaged 56 vehicles.