Beijing is back on the Covid-19 warpath, having renewed restrictions such as shutting schools and locking down housing estates after recording a new cluster of infections tied to a market.

Yesterday, another 31 people were reported to be infected, all linked to the Xinfadi wholesale food market in south-western Fengtai district, taking the total to 137 positive cases since last Thursday.

While there have been no deaths, one person is critically ill.

The flare-up in China's capital has also spread to at least four other provinces - Sichuan, Hebei, Liaoning and Zhejiang.

More than 1,000 flights were cancelled yesterday, after the Beijing authorities elevated its emergency response level to 2, the second highest alert.

It announced it was "strictly controlling" movement in and out of the city. Those deemed to be of medium to high risk are barred from leaving the city, while travellers arriving in Beijing have to be tested and quarantined.

The health authorities warned that the number of infections could persist at this current level for some time, while the country's chief of its Centre for Disease Control and Prevention reportedly said the outbreak could have started a month earlier.