It is the second alert issued in recent weeks, after extreme heat in July saw the UK exceed 40C for the first time. 

The Met Office said while conditions would be below these record highs, the heatwave could be longer. 

More parts of the UK are also facing hosepipe bans amid very dry conditions, as fire crews warn of wildfires. 

The level three heat warning issued by the UK Health Security Agency (UKHSA) covers southern and central England from midday on Tuesday until 18:00 BST on Saturday. 

The amber alert "requires social and healthcare services to target specific actions at high-risk groups", but is one stage lower than the most serous level four red warning issued in last month's heatwave.

A level two yellow alert will be in place for northern England for the same period.

Met Office meteorologist Tom Morgan said a "fairly widespread heatwave" was developing across the UK this week with the peak of the temperatures likely to be on Friday or Saturday.

Temperatures will build from 28C or 29C on Tuesday and reach the low to mid-30s from Thursday, Mr Morgan said.

"It does look like a prolonged period of dry weather and obviously that's bad news for southern England where some rain would really be useful now."

He added the West Midlands and West Country could see with highest temperatures with a maximum of around 35C, but this is uncertain. 

Dr Agostinho Sousa from the UKHSA emphasised it is important to ensure that vulnerable people, like the elderly who live alone and anyone with underlying health conditions, are "prepared for coping during the hot weather".