The Chinese megacity of Chengdu has extended a Covid-19 lockdown in most areas, maintaining curbs that have ground business to a halt and confined the majority of its 21 million residents to their homes.

China is the last major economy welded to a zero-Covid strategy, tamping down virus flare-ups through a combination of snap lockdowns, mass testing and lengthy quarantines.

Chengdu, the capital of southwestern Sichuan province, has been effectively under lockdown for a week since reporting several hundred Covid cases.

The measure was expected to be lifted on Wednesday, but the city government said in a notice that "the entire city will continue to deeply push forward our assault for zero community spread".

Authorities would "strive hard for a week to realise the goal of zero community transmission in the whole city", the government added.

"The fruits of the whole city's anti-epidemic measures are beginning to become apparent, but the risk of community transmission still exists in some areas," it said.

All residents under lockdown will be tested every day, and each household will be permitted to send out one person per day to purchase groceries and other supplies, according to the notice.

Chengdu logged 116 new local infections on Thursday, more than half of which showed no symptoms, according to figures from the provincial health commission.

Confined to their housing complexes, some residents were unable to flee when a strong earthquake in a nearby part of Sichuan reverberated through the city earlier this week, locals told AFP.

China's government has shown few signs of backing away from a zero-Covid approach despite mounting criticism that it is harming growth in the world's second-largest economy.

Businesses in Chengdu have been forced to temporarily close, with Swedish carmaker Volvo last week suspending production at a plant in the city that employs nearly 3,000 people.

Elsewhere, the southern business and technology hub of Shenzhen eased some curbs this week after a virus surge prompted authorities to order the city's 18 million residents to refrain from leaving their homes.

Officials in Beijing have urged the capital to guard against a rebound in infections during the Mid-Autumn public holiday, which runs from Saturday to Monday and is a popular period for travel and social gatherings.

China reported 1,334 new domestic infections on Thursday, the majority of which were asymptomatic, according to the National Health Commission.