(BSS/AFP) - Tokyo recorded on Wednesday the most daily heat-related hospitalisations since 2010, emergency services said Thursday as Japan sweltered in a severe heatwave, with one person dead and four more in a critical condition.

The Tokyo Fire Department said 453 people were taken to hospital on Wednesday, the highest daily count since records began in 2010, with deployments of emergency services the most in at least 63 years.

"We are urging people to stay hydrated and use air conditioners," a fire brigade spokesman told AFP.

"It seems like the number (of patients) rose as the temperature rose. It seems like yesterday and the day before yesterday, we really saw notable increases," the spokesman said.

The fire department also made 3,612 dispatches on Wednesday, the highest since records began for that in 1963, the spokesman added.

He said that one person had died, with four others in a critical condition and 18 in a serious state in Tokyo prefecture -- home to around 14 million people.