A cold snap is expected to worsen the NHS winter crisis for several days from this weekend, doctors are warning.

NHS England says “freezing conditions” are expected to add to the difficulties facing hospitals, which have been struggling for weeks to keep up with a seasonal surge in demand.

“The temperature is set to drop again and looks like it will be below the five degrees mark which statistics show means more illness and more hospital attendances to come,” said Dr Nick Scriven, the president of the Society for Acute Medicine, which represents doctors who specialise in acute and general medicine.

His warning came as NHS England urged people to take precautions against the plummeting temperatures because extreme cold increases the risk of potentially fatal problems such as heart attacks, strokes and breathing trouble.

“The NHS is putting into practice our plan for winter but as temperatures are set to reach below freezing this weekend the public can play their part by keeping warm, stocking up on medications and using NHS Choices and pharmacists to get advice,” said Prof Keith Willett, NHS England’s director of acute care.

The sudden sharp rise in people being hospitalised with flu should prompt anyone who has not yet been immunised to have one, Willett added. “It’s certainly not too late for people to get their flu jab, which is by far the best protection against the flu virus and the really unpleasant consequences which can include hospital admission and even death,” he said.

NHS England also highlighted that “parts of France have reported being on the brink of a flu epidemic”. Last week 24 people in the UK died as a result of flu, compared with seven the week before. The number of flu deaths since October – 48 – is more than double the 23 seen in the same period in 2016-17.

Public Health England said people should keep their homes warm, wear multiple thin layers of clothing and look out for vulnerable friends, relatives and neighbours in the cold spell.

On Friday it issued its fifth winter “keep well warning” since 24 November before the arrival of what in some places will be sub-zero temperatures. Over-65s, young children and anyone with a medical condition should take particular care, it said.

“[People should] ensure they wear lots of thin layers, have plenty of warm food and drinks to stay warm and check weather forecasts before heading out,” said Dr Thomas Waite, of PHE’s extreme events team. He also advised people to wear shoes with good slip-resistant grip, to reduce the risk of a fall, and to stay warm while indoors and keep homes heated to at least 18C.

Scriven criticised the prime minister, Theresa May, and the health secretary, Jeremy Hunt, for denying that the NHS has been in crisis this week. In reality a “system crisis has engulfed the NHS,” with services unable to meet the surge in the demand, he said.

“There has been debate as to what constitutes a crisis but to all those working at the front, for the last four days has definitely been at that level.”

He also castigated Hunt and NHS England for responding to warnings from medical groups in recent months about how tough this winter would be for the NHS with “hot air and rhetoric that is out of touch with activity on the ground and views from the frontline”.

He also criticised the inconsistent application of NHS England’s new policy of cancelling tens of thousands of planned operations and outpatient clinics.