WASHINGTON, US / ISTANBUL

Nine suspects were arrested on Thursday over a deadly blast in northwestern China that claimed the lives of at least 31 people, according to local media.

Authorities are also investigating the cause of the explosion, which occurred at a grill restaurant in the city of Yinchuan, after President Xi Jinping ordered a probe into the incident.

Seven people were injured in the blast and are receiving treatment.

Urging authorities to find the cause of the explosion as soon as possible, Xi said those responsible should be held "accountable in accordance with the law."

He also instructed officials to address "hidden dangers" to ensure the lives and property of residents.

According to China Daily newspaper, the nine people detained by local authorities include the restaurant's manager, as well as shareholders and staff, with their assets also frozen.

The blast took place around 8.40 p.m. local time (1240GMT) on Wednesday, while people were gathering for the start of China's three-day annual Dragon Boat Festival. The holidays begin Thursday.

"All regions and related departments should screen for and rectify all types of risks and hidden dangers," said Xi.

The restaurant was located on a busy street in Yinchuan, the capital of the traditionally Muslim Ningxia Hui Autonomous Region.

Stressing "more efforts to ensure the safety of the people's lives and property," he said: "Relevant departments should launch a campaign to promote workplace safety at an early date and enhance a safety overhaul of key sectors and industries."