Temperatures in urban areas are expected to hover between 6 and 10 degrees on Tuesday, the lowest so far this year.

The Fire Services Department appealed to the public to prioritise their safety and properly assess their capability before they headed for the hills.

Jerry Nip Yuen-fung, chairman of the Fire Services Department Staffs General Association, on Monday said frozen road conditions might delay rescue efforts if people got into trouble.

Nip added people not used to cold weather may underestimate the impact of lower temperatures on their bodies, as well as have insufficient equipment to keep themselves warm and safe.

“Those driving to higher ground may be unaware that there is a possibility that their vehicle engines and water tanks might freeze, but when they try to walk down the mountain, they could slip and fall on the frozen ground,” he said.

He highlighted an incident in January 2016, when 100 people called for help after they headed for 957-metre (3,140 feet) Tai Mo Shan in the New Territories in a bid to catch a glimpse of rare frost that had formed in the sub-zero conditions.

At least 300 firefighters were deployed to rescue people trapped on the hill after they developed hypothermia or injured themselves in the slippery conditions.

A hiker went missing on Tai Mo Shan in sub-zero temperatures last December after he called for help and said he could no longer continue hiking.

Yip said the fire service had bought more cold weather rescue equipment such as crampons, but he pointed out icy roads meant ambulances could not get up steep inclines, which hampered rescue efforts.

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“I hope citizens can consider whether they have the ability or equipment to chase frost as this poses a huge risk to themselves and a huge challenge to the firefighters,” he added. “These people affect society greatly if they persist without thinking through the consequences.”

The Hong Kong Observatory on Monday said temperatures were expected to fall over the next two days because of an intense winter monsoon.

Temperatures in urban areas were expected to drop from 14 degrees Celsius on Monday night to a low of 7 degrees (44.6 Fahrenheit) on Tuesday morning. The mercury in the New Territories is expected to drop even further.

The Observatory, which issued a cold weather warning on Monday morning, said there was a risk of icy conditions on high ground.

Lo Kok-keung, a retired veteran engineer at Polytechnic University, said drivers might lack the experience to cope with freezing conditions because they did not have equipment such as antifreeze for engines and winter tyres.

“If people want to head up Tai Mo Shan, I would advise them to keep their engines running and not stay for too long,” he said.

“This is because their water tanks might freeze in cold temperatures and cars in Hong Kong are not equipped to prevent that.

“Motorists should also drive slowly if the roads start freezing.”

Hong Kong set for very cold start to week; mercury to fall to 7 degrees Celsius

Outdoor experts appealed to people headed outdoors to weigh the risks and make sure they were prepared for bad weather.

Chung Kin-man, a veteran mountaineer and the first Hongkonger to climb Mount Everest, the world’s highest peak, said people could enjoy the outdoors even in cold weather, as long as they had the correct knowledge and prepared well.

“They should not wear clothes that are too thick because the sweat they produce while hiking cannot dry, which will cause them to lose heat even faster,” he explained.

Chung told hikers to protect their heads, necks and hands and take a vacuum flask so they could have hot drinks to help stay warm.

Lobo Louie Hung-tak, a healthcare expert at the Education University of Hong Kong, said the greatest risk in cold weather was the wind chill factor, which could cause hikers to lose body heat fast.

He reminded people who planned long hikes to take enough food and water with them and to stay hydrated, even though they might not feel thirsty.

“Hikers have to evaluate their fitness levels, the quality of their equipment and the cold weather, which may cause hypothermia,” Louie said.

“In cold weather, those with weaker physiques will face a greater risk of cardiac arrest as the cold increases the speed of the expansion and contraction of their blood vessels.”

Louie added winter swimmers should keep their time in the water to less than 20 minutes and to ensure they warmed up as soon as they got out.