<span style="color: #222222;">A group of Japanese doctors today urged Olympic organisers to start the Tokyo 2020 marathon as early as 5.30 a.m., saying failure to do so could lead to deaths from heatstroke.</span><br />'' <br />'' <span style="color: #222222;">The warning is the latest in a chorus of concern about how extreme heat could affect several sporting events at the Olympic games, particularly after Tokyo sweltered through a record heatwave this year.</span><br />'' <br />'' <span style="color: #222222;">The International Olympic Committee (IOC) and Tokyo 2020 organisers have acknowledged the concerns and already moved the marathon start time up 30 minutes to 7:00 a.m., with competitive walking starting even earlier.</span><br />'' <br />'' <span style="color: #222222;">But the Japan Medical Association and the Tokyo Medical Association said that was insufficient because most of the course would still be run in heat levels that were dangerous, and under which physical activity should be halted.</span><br />'' <br />'' <span style="color: #222222;">Heat stroke kills hundreds of people each year across Japan, and this year record temperatures caused a spike in fatalities and hospital visits.</span><br />''