As a heat wave gripped wide areas of the country, at least five people have died due to heat-related causes in Japan since Friday, including an infant left unattended in a parked car for hours, local officials and police said.

In the city of Toyama, 11-month-old Kokomi Nobata was confirmed dead in hospital after her mother left her strapped in a child seat in the back of her vehicle for about four hours.

Police arrested Suzu Nobata, the 25-year-old mother who told police officers she had used a proxy driving service to return home after drinking at a restaurant early Friday.

The police believe the mother came home around 5:20 a.m. Friday and did not realize she had left her daughter in the car until around 9:30 a.m. The temperature had risen to close to 32 C in Toyama by around that time, according to a local weather observatory.

In Ageo, north of Tokyo, a man in his 60s was found collapsed in front of his house Friday afternoon, local officials said Saturday. He is believed to have died due to the heat, they said.

After a family member made an emergency call in Miyagi Prefecture early on Saturday, a woman in her 80s was taken to hospital where she was later confirmed dead, according to responders. The hospital concluded her death was heat-related, they said.

In Nagasaki and Tochigi prefectures, the deaths of an 83-year-old woman and a man in his 90s were blamed on the extreme heat, according to local officials.

The central government has said nearly a dozen people have died recently due to heat-related medical issues as temperatures rose sharply following the end of the rainy season in most areas.