China has reported more local symptomatic COVID-19 cases so far this year than it recorded in all of 2021, as the highly transmissible Omicron variant triggers outbreaks from Shanghai to Shenzhen.

Mainland China reported 1337 new domestically transmitted COVID cases with confirmed symptoms on March 13, the National Health Commission (NHC) said on Monday.

That brought the total this year to more than 9000, compared with 8378 in 2021, according to Reuters calculations.

"China's economy could be severely hit again," said Nomura in a note, adding that the COVID situation in China had deteriorated at an "alarming" pace over the past week.

"The outbreak has now reached almost every part of China with significant economic importance."

Officials in Shenzhen, China's Silicon Valley, have temporarily suspended public transport and urged people to work at home as they carry out city-wide testing this week following a surge in new cases.

Apple suppliers Foxconn and Unimicron Technology Corp both suspended operations in the southern city on Monday. Foxconn, formally known as Hon Hai Precision Industry Co, said operations would be suspended until further notice, adding it would deploy backup plants to reduce the disruption to production.

In the northeastern city of Changchun, which is currently under lockdown, Toyota suspended production at its joint venture with China's FAW Group.

Including cases arriving from outside the mainland, China reported 1437 new confirmed COVID cases on March 13, the NHC said, compared with 1938 a day earlier.

There were 906 new asymptomatic cases, which China does not classify as confirmed cases, compared with 1455 a day earlier.

There were no new deaths, leaving the death toll unchanged at 4636.

As of March 13, mainland China had reported 116,902 cases with confirmed symptoms, including both local and imported ones.