“It will be windy with a few rain patches,” the forecaster said. “The minimum temperature will fall to around 7 degrees in the urban areas, and a couple of degrees lower in the New Territories.”

The mercury hovered around 10 to 14 degrees in urban areas on Monday evening, but dropped to as low as 2.1 degrees in Tai Mo Shan and 6.3 degrees in Ngong Ping.

The Senior Citizen Home Safety Association, which operates a “safety phone” service that delivers fast care-on-call help, said they took 1,325 calls over the 12 hours up to 6pm on Monday.

There were 53 people treated in hospital, most of them for dizziness and chronic pain.

The organisation handled 1,218 calls over the same period on Sunday and 32 people needed hospital treatment.

“The association anticipates an increase in the number of requests for assistance received by the support centre, and has already made early preparations to provide comprehensive support to the elderly during the severe cold weather,” it said.

“A severe cold may lead to the death of frail, elderly people and the public should pay attention to their health condition.”

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

Family doctor Lam Wing-wo warned that people should pay close attention to elderly relatives over the next few days because they were more vulnerable to hypothermia and to a deterioration in existing health conditions.

He said those who lived alone or were from poorer socio-economic backgrounds were especially at risk.

“We have to be really careful about any minor changes in their body, such as a loss of appetite … they may mean something already very serious, like hypothermia, or stroke, or heart attack,” Lam said.

He added outdoor exercise could have beneficial effects for the elderly by helping them to generate heat and increase their energy levels.

But he emphasised it was important for them to maintain their body temperature by dressing in appropriate clothes for the weather and remaining hydrated with warm water.

Lam added that the elderly should also be accompanied when exercising and be careful about any health conditions they already had.

Authorities also warned vulnerable groups, including the elderly and those with pre-existing medical conditions, to protect themselves from the cold.

“Elderly people have less insulating fat beneath their skin to keep them warm and their body temperature control mechanism may be weaker,” a Centre for Health Protection spokesman said. “Their bodies may not be able to appropriately respond to the cold weather.”

Chronic conditions such as hypertension and diabetes could affect the health of elderly people and lower their metabolic rate, causing their bodies to generate less heat, it added.

The cold weather could also aggravate the effects of such diseases among younger patients, the centre said.

Temporary shelters across the city will remain open until the cold weather warning is lifted.

The flu season had also started in Hong Kong and is co-circulating with Covid-19, Professor Ivan Hung Fan-ngai, a top infectious diseases expert at the University of Hong Kong, warned.

Hong Kong braces for cooler weather at 8 degrees Celsius early next week

He said it was important for high-risk groups to get their influenza jab and Covid-19 booster targeting the XBB variant at least two weeks before the Lunar New Year holiday next month.

That should include healthcare workers, those with chronic illnesses, the elderly in care homes and care home workers, Hung added.

“We expect the number of severe cases of influenza to rise after the Lunar New Year due to the large movement of the population in Hong Kong and the mainland,” he said.

The cooler weather is expected to continue until Thursday, but the mercury was expected to start climbing again after that.

The Observatory said temperatures across the city on Wednesday would range from 8 to 12 degrees, vary between 11 and 16 degrees on Thursday and reach 13 to 18 degrees on Friday.

Temperatures are also expected to climb over the weekend, up from a low of 13 degrees on Friday to 18 degrees next Monday and Tuesday.