The 2021 Shanghai Marathon has been indefinitely postponed, organisers said on Wednesday, citing a resurgence of the coronavirus that also has forced the suspension of the Beijing and Wuhan marathons.

China is battling a fresh Delta-driven outbreak that has spread across the country and sparked tough new measures to stamp out the virus before the Beijing Winter Olympics in February.

"Today, we've chosen to be cautious. We've chosen the health and safety of runners and citizens," organisers of the November 28 race said on an official social media account.

A new date would be announced in the future, it said.

The announcements did not say how many runners were due to compete, but said that around 9,000 took part in last year's event.

Organisers of the Beijing and Wuhan marathons both announced last month that those races were also postponed due to the outbreak.

Although China's case numbers remain relatively low -- it reported 54 new infections on Wednesday -- China takes a zero-tolerance approach toward the coronavirus and the government is especially concerned over any impact on the February 4-20 Winter Games.

Authorities have implemented mass testing, targeted lockdowns, and have suspended some cross-provincial tour groups and closed tourist sites.