A blast at a fireworks factory in China’s Hunan province has killed 21 people and injured 61, prompting a call from President Xi Jinping for a thorough investigation, state media reported on Tuesday.

The explosion in Liuyang, under the administration of Hunan’s capital city of Changsha and a hub for fireworks manufacturing, occurred on Monday at around 4:40 pm (0840 GMT), according to reports by CCTV and Xinhua.

Social media footage showed massive plumes of smoke billowing up into clear blue skies against a backdrop of lush, green mountains.

Reuters verified the location shown in the footage, which was posted on social media on May 4, as Changsha.

A Xinhua video showed thick clouds of smoke rising from a large site littered with collapsed buildings and debris.

Five rescue teams of nearly 500 personnel, together with three rescue robots, were dispatched to the scene, adopting a “human machine coordinated approach” to conduct grid-style searches, according to Xinhua.

Two black powder storage warehouses within the factory compound posed high-risk hazards, the report said, adding that authorities had evacuated residents from danger zones, established a 1 km rescue area and a 3 km control zone.

The blast happened at Huasheng Fireworks Manufacturing and Display Company, state media said.

Reuters could not find a telephone listing for the company to seek comment.

The person in charge of the company has been detained and the cause of the accident was being investigated, state-run China Daily reported.

Xi called for a speedy investigation to determine the cause of the explosion and strict accountability for the incident, Xinhua reported.

Last year, China exported $1.14 billion worth of fireworks, more than two-thirds of global sales, data from the Observatory of Economic Complexity showed.

Xi also ordered authorities to strengthen risk screening and hazard control in key industries, enhance public safety and ensure the safety of people’s lives and property.

Xi often issues “important instructions” to local officials after major accidents and disasters with fatalities.

Last week, he urged a nationwide upgrade in China’s disaster response capacity.

Xi also issued instructions after a fire tore through several residential towers in Hong Kong’s Wang Fuk Court complex in November killing 168 people.