Major Chinese manufacturing province Zhejiang is fighting its first COVID-19 cluster this year, with tens of thousands of citizens in quarantine and virus-hit areas suspending business operations, cutting flights and cancelling events.

The province reported 74 locally transmitted cases with confirmed symptoms on Dec. 12, official data showed on Monday, almost double the previous day's 38 cases, lifting to 173 the total since the province started to report cases for the latest outbreak.

The outbreak in three Zhejiang cities - Ningbo, Shaoxing and Hangzhou - was developing at a "relatively rapid" speed, while the situation nationwide was largely stable, National Health Commission official Wu Liangyou said on Saturday.

Before the current outbreak, Zhejiang - home to a legion of small and medium-sized enterprises, many of which are exporters - reported only one local case in 2021.

More than a dozen Chinese-listed companies said they had suspended production in parts of Zhejiang owing to tightened COVID-19 curbs.

Outbreaks in dozens of Chinese cities this year remained smaller than many overseas, but local governments were told to ensure infections are detected and contained as early as possible to prevent further spreading, triggering curbs that have led to occasional disruption to travel and tourism.

Flights leaving Ningbo Lishe International Airport to Shenzhen city were suspended from Sunday, while flights to Beijing were cancelled from Dec. 6. Only one daily flight from Hangzhou to China's capital is allowed.

More than 50,000 people in Zhejiang have been quarantined at centralised facilities and nearly half a million people's health condition were monitored, a province health official said on Monday. The coastal province has a population of 64.6 million.

Zhejiang has ordered travel agencies to suspend organising tourism trips linking the province and other areas and has also halted province-level sports events.

Wenzhou and Yiwu, two cities in Zhejiang yet to report local cases from the latest outbreak, ordered the closure of entertainment venues such as bars and chess and card parlours.

Apart from the 74 local symptomatic infections in Zhejiang, Shaanxi province and the northern Chinese region of Inner Mongolia reported one and five local cases respectively on Sunday.

As of Dec. 12, mainland China had 99,780 symptomatic cases, including those arriving from abroad. The death toll remained unchanged at 4,636.