Hong Kong's athletic and swimming bodies slammed local authorities on Wednesday for imposing last-minute pandemic restrictions on the size of two major upcoming races, in the latest blow to the city's sporting reputation.

The rare public rebuke comes as Hong Kong's new government vows to reopen the international hub — including for sports — while maintaining strict controls under China's zero-Covid demands.

The Hong Kong Association of Athletic Affiliates (HKAAA) and the Hong Kong China Swimming Association (HKCSA) released a joint statement to "place on record their disappointment" over restrictions the city's government requested for two events to go ahead.

A 10-kilometre run planned for Sunday with up to 2,500 participants was cancelled by the HKAAA on Wednesday after the government "drastically reduced" the race quota despite months of negotiations.

Meanwhile the HKCSA, which organises an annual cross-harbour race in October, has said it will likely cancel after being told a maximum of 500 swimmers can take part instead of the hoped-for 1,500.

"These short notice decisions are of great concern to both parties and create major issues for those responsible for organising these high profile public sporting events in Hong Kong," the statement read.

A government spokesperson defended the decision to cap the race sizes.

"The risk of infection is rather high so the exempt for group gathering is temporarily withheld," the spokesperson said.

Like China, Hong Kong is still hewing to mandatory quarantine for arrivals and controls on large gatherings, measures that have kept the city cut off during the pandemic and hammered the economy.

Newly appointed city leader John Lee has said he wants to "open a new chapter for Hong Kong" and restore its reputation as an international hub.

But he must also meet Beijing's requirements to keep cases low in a bid to seek a reopening of the border with the mainland.

Hong Kong is set to welcome back the Rugby Sevens after a three-year break in November, although officials have said teams will have to live in a closed loop and there will be restrictions on where spectators can eat and drink.

A summit for the financial industry is also planned for November. But it is not yet clear if quarantine will be lifted.

Currently all arrivals to Hong Kong must undergo three days of mandatory hotel quarantine and four days of restricted movement afterwards.