Japan is considering adopting daylight saving time next year so that athletes in the 2020 Tokyo Olympic Games can compete in cooler hours, reports say.

The proposal to bring clocks forward by two hours has received major opposition on social media with many worried it would result in longer working hours.

At least 120 people have died in a record heatwave since July.

The government says it is yet to decide on the move but does want to limit the effect of summer heat on the athletes.

"It is not true that the government has decided to aim for adopting daylight saving time," Chief Cabinet Secretary Yoshihide Suga told a news conference. He said such a move would have a "major" impact on people's lives.

"We plan broad measures such as earlier start times, more greenery and heat-inhibiting pavements," he added

The 2020 games, which will be held in late July and early August, fall during the country's hottest and most humid months.

Olympic officials had early appealed to Japanese Prime Minister Shinzo Abe to adopt daylight saving time so that events like the marathon could be scheduled in the cooler morning hours.