Standard Chartered marathon runners will have to keep masks on at the start and can only remove them after a certain distance.
That indication came as co-organizer Hong Kong Association of Athletics Affiliates faced up to local nervousness of a possible community outbreak of the highly contagious Delta Covid
The additional measure comes after organizers said on Wednesday that runners would have to be fully vaccinated and get nucleic acid test reports two weeks and 72 hours before the race.
The marathon, scrapped last year and to be held October 24, will see just 18,500 participants, compared to 74,000 in 2019.
Association executive director Dennis Ng Yu-ho said: "After they have run about half the distance, staff will inform runners they can remove masks. And after they cross the finish line, they will be given fresh masks."
Recycling bins would be in place for mask disposals.
Runners would not need to gather and vie for the best start.
"The numbered cloth on each runner's top comes with a chip, which will record their starting time once they run past a rug with a built-in stopwatch," Ng said.
A "streamlined" tactic will be used, with space between contestants maintained during the race.
A rug with a built-in stopwatch will be there to record finishing times.
More than half of the 18,500 quota will be reserved for those signing up for last year's race, with their registration being from Monday to Friday next week.
The rest will be open on a first-come-first-serve enrolment from September 2.
Organizers are looking at inviting overseas runners. "The government hopes organizers will only invite runners from 'low-risk countries," Ng said.
University of Hong Kong microbiologist Ho Pak-Leung suggested runners take rapid antigen tests on the day of the race.
Ho said the infection-control measures were still not enough, calling for post-marathon testsing for runners in the event of an outbreak.