Four people died and 40 others suffered heatstroke on the job during July's unprecedented heat wave, according to data released Wednesday by the Health, Labor and Welfare Ministry.
The preliminary figure is already triple that of the same month last year, when 13 people suffered heatstroke at work.
By occupation, the largest number of victims was from the construction industry at 27, including the four who died. This was followed by six security guards and four delivery service workers.
The data were compiled from reports by companies to labor bureaus on job-related compensation applications that involved four days or more of absence from work due to heat stroke.
The ministry said the number might increase in August and September. It urged workers to drink a lot of water and take breaks when working in hot weather.
Cool Tokyo campaign
Under the scorching sun, crowds clad in traditional "yukata" cotton robes gathered Wednesday in the Odaiba waterfront area to kick off a weeklong campaign of sprinkling water on asphalt and concrete to cool down Tokyo.
With buckets of water recycled from a nearby hot spring facility and the Ariake Waste Water Treatment Plant, about 250 people splashed water on the pavement in a tradition called "uchimizu," practiced since the Edo Period.
Tokyo has been sizzling through a heat wave over the past two months, with the mercury shooting up to 39.5 on July 20 during a record-breaking streak of 40 straight days of temperatures over 30 through last Saturday.