The possibility of extreme summer heat and typhoons in Tokyo is a "major issue" for the 2020 Olympics, a top official said Thursday, admitting there would be a knock-on effect on the budget. Speaking to bosses from Olympic Committees around the world, Tokyo CEO Toshiro Muto said the Japanese capital had endured "unprecedented heat weather and typhoons last summer." "Tokyo 2020 considers those as major issues," said Muto, adding that organisers and the International Olympic Committee (IOC) were working together on ways to mitigate the impact on athletes and fans. IOC chief Thomas Bach said on Wednesday that medical experts were proposing measures to protect competitors and supporters throughout the Games. Tokyo sweltered through a series of deadly heatwaves last summer, raising concerns for the wellbeing of athletes, especially competitors of endurance events such as the marathon and race walking. Organisers have already brought forward the marathon start time to 7am to get cooler conditions but officials are considering bringing the event even further forward. Japanese medical groups have suggested that failure to start the marathon earlier could "lead to deaths" from heatstroke. When Japan last hosted the Olympics, in 1964, the Games were held in October to avoid the country`s stifling summer humidity and heat. Muto said he would transmit weather data to national Olympic Committees to help their athletes prepare for the conditions they are likely to face. Speaking to reporters afterwards, Muto acknowledged that measures to beat the heat had increased demands on the budget. Organisers plan countermeasures from solar-blocking paint on roads to mobile misting stations. The CEO said that while the heat countermeasures could boost the budget, Tokyo 2020 had been able to make cuts in other areas. Tokyo 2020 was "absolutely determined" that the next version of the budget, due to be unveiled next month, would not exceed the $12.6 billion earmarked last year to pay for the Games, Muto said. The CEO laid out a rosy picture of preparations for the Games, with just more than 600 days to go until the Opening Ceremony. "Venue construction is on track and will be completed in time for the test events," which will take place in the run-up to the Games. IOC chief Thomas Bach said Wednesday: "I do not remember any host city which was so far in its preparations two years before the Olympic Games than Tokyo."