Beijing authorities have sealed off a mall and locked down several residential compounds over a Covid flare-up, as the latest outbreak spread to the Chinese capital's central districts.

China has largely curbed widespread transmission of the coronavirus through snap lockdowns, mass testing and travel restrictions, but authorities are on high alert after a nationwide spike linked to domestic travel in the past month.

Six new cases were found in Beijing's central districts of Chaoyang and Haidian Thursday morning, local media reported, all close contacts of people infected recently in northeastern Jilin province.

Raffles City mall in Dongcheng -- also a central district in the capital -- was sealed off Wednesday evening after a close contact of a person with Covid-19 was found to have visited the mall, the Beijing Youth Daily reported.

Its exits were closed, and all staff and customers inside were not allowed to leave until they got tested.

Videos shared on social media platform Weibo showed crowds of shoppers in masks, lining up to be tested inside the shopping centre.

The mall remained closed Thursday.

The latest spike occurred during a high-level meeting of top Communist Party leaders in Beijing.

Beijing health officials said at a briefing that more than 280 close contacts have been identified, with almost 12,000 people screened for the virus in both Chaoyang and Haidian districts.

"This cluster outbreak was sudden with many places covering a large area. It involves many people, and prevention and control is very difficult," said city government spokesman Xu Hejian.

"Today is a crucial day... and it is necessary to trace the source of the outbreak as soon as possible."

Five residential communities, a primary school and two office compounds were placed under snap lockdowns early Thursday, with tens of thousands of residents barred from leaving and made to undergo mass testing.

Live streams on local media of the areas under lockdown showed staff in hazmat suits piling up bags of food for residents stuck inside.

Four of the diagnosed cases are members of the same household, while the other two are a Jilin resident on a business trip to Beijing and their close contact, local health authorities said.

As more nations lift coronavirus restrictions, China continues to pursue a strict zero-Covid strategy that has seen its international borders largely closed since the start of the pandemic.

Its latest wave of infections has seen millions put under lockdown and domestic travel rules tightened, with many flights and trains cancelled.