Torrential downpours around Britain left three dead and hundreds stranded on Monday as storms continued to batter Russia and a heatwave in southern Europe led to further deaths and sparked fires.

Several hours of effort from rescuers including police divers was not enough to save a 28-year-old man in Hull, northwest England, who died after becoming trapped while trying to clear a flooded drain.

Local police in nearby Sheffield said later they had recovered the body of an unidentified young man, though his body was found downstream from where a teenage boy was earlier reported to have been swept up by the floods.

They also confirmed that a 68-year-old man was killed in the city as he got into difficulties attempting to cross a flooded road.

Hundreds of people were stranded in Sheffield, where military and police helicopters were scrambled to help rescue people trapped in cars or taking refuge from the fast-rising floodwaters on rooftops.

"It's very difficult to get an actual understanding of how many people, but we are talking in the hundreds of people affected by this sea of flooding," said emergency coordinator Flight Lieutenant Ronnie Metcalfe.

Metcalfe, speaking from a Royal Air Force base in Scotland, added that the number of people in bad trouble was continuing to rise through the evening as reports came in of thousands of people being without power.

Britain's Environment Agency, which monitors weather risks nationwide, issued 16 severe flood warnings and 102 standard flood warnings throughout the country.

Russia was experiencing similarly chaotic weather, with four people dying in storms that hit the south of the country, part of the mountainous Ural area, western Siberia and parts of Siberia close to Mongolia.

Conditions were radically different in southern and eastern Europe and in the Mediterranean, where a heatwave was sparking fires fanned by strong southerly winds known as the sirocco.

Helicopters and other aircraft joined firefighters on the ground in southern Italy battling around 25 fires in Calabria, Sardinia and on the island of Sicily.

The situation was particularly serious in Sicily, where according to media reports guests at a number of hotels near the northwest coast had to be evacuated.

A heatwave in Greece killed two pensioners at the weekend and pushed demand for electricity to new all-time highs, officials and news reports said.

Hospitals around the country have been placed on alert and municipalities are keeping cooled public facilities open for those without air-conditioning at home.

The move came too late for an 84-year-old woman in the western town of Egio and a 76-year-old man in Farsala, central Greece who both succumbed to heatstroke.

Temperatures were expected to reach 43 degrees Celsius (109.4 Fahrenheit) in some areas on Monday and to remain around that level during the week, the Greek weather service (EMY) said.

On the island of Cyprus a 72-year-old woman died of heatstroke on Monday as the holiday island sizzled in temperatures above 40 degrees Celsius.

The Mediterranean island is famed for its year-long sunshine but temperatures of 42 degrees now being recorded in the capital are extreme.

In Romania the capital Bucharest and eight southern districts were placed on orange alerts as the temperature headed above 40 degrees Celsius.

The heatwave that has already lasted several days has taken at least 25 lives.

First aid tents have been erected in many cities while ambulance services have received thousands of calls.