Dozens of shattered runners had to be stretchered away from the finish line after completing the hottest ever London marathon today.

Many exhausted competitors collapsed to the ground after running the 26.2 mile course in the sweltering heat, while others stood in front of fans as they desperately tried to cool down.

Mobile water stations had to be dispatched to provide runners with water after stations between miles eight and ten ran out.

Race organisers had previously urged runners to reconsider aiming for personal bests and suggested ditching fancy dress costumes amid the unseasonably warm April weather.

It was the hottest London Marathon on record with the temperature reaching 23 degrees Celsius - although it was estimated to be even hotter on the tarmac.

A runner is stretchered across the line by medical staff during the 2018 Virgin Money London Marathon, Sunday April 22, 2018. Photo / AP

Sir Mo Farah broke the British marathon record today but lost his cool after complaining that race stewards were too busy taking pictures of him, they forgot to hand him water.

Farah was irritated at not being able to find the right water bottle at two drink stations early in the race.

At one point he was even seen remonstrating with the motorcyclists travelling alongside the runners.

'The drink station was confusing,' he added. 'The staff were helpful at the end but at the beginning they were trying to take a picture rather than giving me the drink.

'I was saying to the people on motorbikes to tell the staff to be a bit helpful. I wasn't wasting energy, I just needed a drink. I had to get it right.'

Meanwhile, Paula Radcliffe's world record survived as Vivian Cheruiyot timed her run to perfection to win the women's race.

Cheruiyot, 34, took advantage of failed attempts by last year's winner Mary Keitany and runner-up Tirunesh Dibaba to break Radcliffe's 15-year-old mark.

Once again the conditions told as first Dibaba, of Ethiopia, and then Cheruiyot's fellow Kenyan Keitany fell away allowing the 2016 Olympic 5,000 metres gold medallist to claim victory.

Lily Partridge was the first British woman over the line in eighth place.

The hottest-ever London Marathon featured a Kenyan double as Eliud Kipchoge swept to a third victory in front of Buckingham Palace joining Vivian Cheruiyot who won the women's race on Sunday.

The 33-year-old Kipchoge ran the 26.2-mile (42.2-kilometer) course in 2 hours, 4 minutes, 27 seconds to add to the Olympic champion's wins in the British capital in 2015 and 2016.

Kenya's Eliud Kipchoge reacts after crossing the finish line to win the Men's race in the London Marathon in central London, Sunday, April 22, 2018.(AP Photo/Kirsty Wigglesworth)

"I ran a really beautiful race,'' he said.

Tola Shura Kitata of Ethiopia was second, followed by Mo Farah, who set a British record 2:06:21 in front of his home fans who lined the streets in temperatures that reached 23.2 Celsius near the finish.

While the race began in the southeast London district of Blackheath, the official starter for the men's race was more than 48 kilometres to the west of the British capital. Queen Elizabeth II pushed the start button in front of Windsor Castle.

The race ended in front of the monarch's London residence - Buckingham Palace.

Cheruiyot, the Olympic 5,000-meter champion, crossed the line in 2:18:31 seconds to win at her second attempt. Fellow Kenyan, Brigid Kosgei, was 1 minute, 42 seconds further back and Tadelech Bekele of Ethiopia was third.

There was a home success with David Weir winning the men's wheelchair race for an eighth time after a sprint finish.

The 38-year-old Weir clocked 1:31:15 to beat Marcel Hug of Switzerland into second place, while Daniel Romanchuk of the United States was third.

Madison de Rozario of Australia won the women's wheelchair race for the first time ahead of four-time champion Tatyana McFadden, whose fellow American, Susannah Scaroni, was third.