Intensive efforts to wipe out mosquitoes along the Tsing Yi Nature Trails will take a week to 10 days, an official said on Wednesday, a day after the area was closed over a chikungunya fever outbreak.

Five people who have come down with the illness are suspected to have been infected while hiking along the trails.

The authorities say hundreds of potential breeding sites have already been eliminated, with foggers, larvicides, traps and robot dogs deployed in the fight to kill the mosquitoes.

But challenges remain, according to Albert Au, who heads the Centre for Health Protection's communicable disease branch.

"The main reason is that the Tsing Yi Nature Trails cover a vast area. It is seven kilometres long," he told RTHK.

"When we inspected the area with the Food and Environmental Hygiene Department, we found that some stormwater drain outlets were blocked by fallen leaves and branches. These challenges may make it more difficult to prevent and control mosquitoes."

Au said any chikungunya-carrying mosquitoes along the trails are unlikely to infect people in urban areas because they cannot fly that far.

He urged people who have hiked in the area recently to pay attention to any health conditions and see a doctor as soon as possible if they develop symptoms such as fever or joint pain during the two-week incubation period for the illness.