The heat is on: Tokyo 2020 marathon to start earlier

The Tokyo 2020 Olympic marathon will start between 5:30am and 6am, organizers announced Wednesday, after experts raised concerns over the health of competitors and fans during the city's sweltering summer heat.

An expert medical committee had proposed a start time "between 5:30am and 6am", top Olympic official John Coates said after a series of meetings in the Japanese capital.

Organizers had already brought the marathon forward to 7am as Japanese medical groups have warned the event could "lead to deaths" from heatstroke.

Tokyo 2020 organizers still need to agree with the International Association of Athletics Federations before fixing the exact time, said Coates, who is chairman of the Olympic coordination commission.

Rugby sevens matches will also start 90 minutes ahead of schedule and mountain biking an hour later to avoid the burning sun. The 50-kilometre race walk will also be brought forward.

The Japanese capital sweated through several deadly heatwaves this summer as Japan was also battered by a series of typhoons that caused death, destruction and delay.

Coates said a series of anti-heat measures was being planned, including mist sprays along the marathon route and heat-absorbing paint on the roads.

There is also an increase in medical facilities as a precaution and more shade for fans lining up for entry to the venues.

"There is a list of about 20 precautions they (the medical commission) think we should take and they are not going to be free," quipped Coates.