Temperatures in the UK have dropped to below freezing in some parts of the UK this week.
Commuters could see major disruptions as frost and ice sweeps the country.
Officials have warned the elderly – and those with underlying health conditions – to take extra care.
The cold weather could also increase the risk of becoming infected with flu, the NHS warned.
“Some health problems, such as asthma, sore throat and cold sores, are triggered or worsened by cold weather,” said the NHS.
“Flu can be a major killer of vulnerable people.
“People aged 65 and over, pregnant women and people with long-term health conditions, including diabetes, kidney disease and chronic obstructive pulmonary disease, are particularly at risk.”
Signs of flu include a sudden fever, headaches, sore throats and a dry, chesty cough.
The viral infection could also lead to loss of appetite, diarrhoea, muscle aches, and vomiting.
The best way to prevent flu during the cold weather is to get the flu jab, the NHS said.
If you’re over 65, or have a long term health condition, you’re eligible to the pneumococcal vaccine, which could help to protect against pneumonia.
You could also prevent infection by regularly washing your hands, and avoiding crowded spaces.
Cold weather also increases the risk of other deadly conditions.
Heart attacks, arthritis and norovirus are more common during periods of cold temperatures.
Meanwhile, it was also revealed this week that record numbers of people have died unnecessarily in cases related to the cold weather.
The Met Office expected the cold weather to last all this week, with some fears it could last for another month.