TOKYO (Reuters) - Japan warned on Tuesday against the risk of heatstroke in Tokyo and areas in its east and west, as hot and humid conditions behind several recent deaths drove some people to use new "cooling shelters" set up around the capital.

Authorities urged people to avoid physical activity as the environment ministry issued top 'danger'-level alerts, while media said scores of people were hospitalised, with some dying from heatstroke symptoms over the last few days.

"It's a life-threatening emergency," said 60-year-old Hisako Ichiuji, who resorted on Tuesday to a "cooling shelter" at the capital's Tokyo Tower, a popular tourist spot.

Typically facilities such as community centres or libraries equipped with air conditioners, the shelters are part of a scheme adopted this year requiring local governments to provide people a respite from the heat after warnings go out.

"(In the past) the temperature wasn't like this," Ichiuji added. "I think it's important to keep ourselves hydrated, and take shelter in a facility like this."

An 86-year-old farm worker was found dead on Monday in a field in the southwestern Fukuoka region, surrounded by towels and bottles of water, the Asahi newspaper said.

Temperatures hit a record 40 degrees Celsius (104 degrees Fahrenheit) on Monday in the city of Shizuoka, while other areas, some in Tokyo, have witnessed record temperatures for this time of year.

As demand soared, Japan's biggest power provider, JERA, increased output at some plants and pulled back online some it had halted for maintenance, to help those struggling to beat the heat.

TEPCO, the main electricity provider to Tokyo, had to buy power from another utility to prepare for an expected surge in demand.

On Tuesday, Trade Minister Ken Saito said the government was monitoring the situation "with a sense of urgency" and would take every step to ensure stable electricity supply.

The farming and fishing industries are preparing for the impact of rising temperatures, which the agriculture ministry said this month were affecting the quality of staples such as rice and thinning the catch of some fish, such as salmon.

(Reporting by Irene Wang; Additional reporting by Tim Kelly; Writing by John Geddie; Editing by Clarence Fernandez)

By Irene Wang