The first yellow heat-health alert of the year has been issued for London and other regions by the UK Health Security Agency (UKHSA).
The alert is currently in place from 9pm on Thursday 12 June to 8am on Sunday 15 June and covers the East of England, East Midlands, London and South East regions.
It comes as tempertaures are to soar, with 27C predicted in the capital. The UKHSA said the Met Office has warned that temperatures of up to30C could be seen in parts of England.
Under UKHSA and the Met Office's Weather-Health alerting system, a yellow alert means that there could be an increased use of health care services by vulnerable populations.
It may also lead to an increase in risk to health for individuals aged over 65 years or those with pre-existing health conditions, including respiratory and cardiovascular diseases.
Dr Agostinho Sousa, head of Extreme Events and Health Protection at UKHSA, said: "Our findings shows that even moderate heat can result in serious health outcomes, especially for older adults, and it is therefore important that everyone takes sensible precautions while enjoying the sun.
"The forecasted high temperatures are expected to be short-lived but could primarily impact those over the age of 65 or those with pre-existing health conditions.
"If you have friends, family or neighbours who are more vulnerable, it is important to check in on them and ensure they are aware of the forecasts and are following the necessary advice."
A yellow alerts for thunderstorms has also been issued for London from 3pm on Friday until 6am on Saturday.
It warned flooding and spray on roads could lead to difficult driving conditions, while train and bus services could face cancellations.
It said there was slight risk of power cuts and flooding to homes and businesses.
A thunderstorms warning is also in place for the south west on Thursday.
