At least five people have died in eastern Japan after “unprecedented” heavy rain that left nearly 7,000 stranded at Tokyo’s Narita airport and forced thousands to take refuge in government buildings.

The torrential rains hit Chiba prefecture, east of Tokyo, on Thursday night, triggering landslide warnings and power outages. Evacuation orders were issued for more than 400,000 people in Chiba and other areas, and about 45,000 homes lost power, as 115mm of rain fell hourly, approximately the same amount usually recorded for the whole month of August.

It was the first time the Japan Meteorological Agency has issued the highest level-5 warning for heavy rains and landslides for the prefecture.

The body of a man, believed to be in his 60s or 70s, was found floating in a flooded road in the city of Ichikawa, while a 66-year-old woman was killed when her car got trapped in flood waters in the city of Sakura. Two other people are reported to have died after being unable to escape from their cars during the flooding. Soldiers have been dispatched to the area ‌to help with relief efforts.

“This case was an extremely unusual situation,” Chiba governor Toshihito Kumagai told reporters on Friday morning. “I have responded to many disasters in the past, but I have never experienced a case like this.”

A makeshift evacuation centre set up at the Chiba prefectural government building after transport was disrupted by the torrential rain. Photograph: Kyodo/Reuters

Approximately 7,000 passengers spent the night at Narita, one of Tokyo’s main international airports, while 1,700 people sought shelter at the Chiba prefectural government building.

Footage from public broadcaster NHK showed water spurting violently from what appeared to be a maintenance hole and exceeding the height of a nearby five-storey building in Chiba’s central ward.

Flooded areas after heavy rain in Chiba prefecture. Photograph: Kyodo/Reuters

A woman in Ichikawa told NHK the rain “happened all of a sudden so it was a complete surprise”.

“The power is out so I’m worried whether I can open my business in the next couple of days,” she said.

A traveller from the UK who gave his name as Philip told AFP that he had to go through a nine-hour journey, including a taxi ride, before finally arriving at the airport early on Friday morning.

With a sleeping bag in hand, he said he has “just been trying to get some sleep and watching Netflix”.

“Just get on with it, really. Nothing else you can do,” he said.

Rain had eased by Friday but authorities are warning of the dangers of flooding in the area.

“For rivers where the risk of flooding is already high, please take action to protect your lives in any way possible,” said Kazuhito Shimamoto of the ministry of land, infrastructure, transport and tourism.

“There are also rivers where the risk of flooding is expected to increase further, so please check the evacuation advisories issued by your local municipalities and evacuate early.”

Meteorologists in Japan say that climate breakdown is increasing the frequency and intensity of extreme weather events.

Reuters and Agence France-Presse contributed to this report