A major explosion hit China’s eastern port city of Ningbo on Sunday, sending dozens to hospitals, destroying vehicles, and triggering the collapse of nearby buildings, state media said, citing local authorities.

The morning blast occured in a factory, according to the official Xinhua news agency, but state television said it took place at a demolition site.

Television images showed cars twisted and mangled by the force of the explosion, a plume of grey smoke rising in the sky, and debris scattered for dozens of metres around the site of the incident.

Footage showed rescuers wearing helmets carrying injured people away from the area, while others stood over a person lying on the ground.

According to CCTV, eyewitnesses said there were “a large number of injured people” in the city, one of China’s largest ports, which sits just south of Shanghai.

At least 30 people were taken to the local hospital and rescue efforts were continuing, the report said.

The Communist Party’s People’s Daily said on Twitter that no one lived at site of the explosion but garbage collectors might have been working there.

An enquiry has been launched to determine the cause of the explosion, the local police in Jiangbei district, where the blast happened, said on social media.

Industrial accidents are common in China, where safety standards are often lax.

In 2015, giant blasts killed at least 165 people in the northern port city of Tianjin, causing over $1 billion in damage and sparking widespread anger over a perceived lack of transparency by officials about the accident’s causes and environmental impact.

A government inquiry into the Tianjin accident released in February 2016 recommended 123 people be punished.

The official who was mayor at the time of the accident was sentenced to 12 years in prison for graft in September.

Huang Xingguo, 62, had also headed the disaster response committee.