A fire ripped through more than 170 buildings and killed one person in a southern Japanese coastal city on Wednesday, with military and firefighting helicopters scrambling to extinguish the country's largest urban blaze in almost half a century.

Aerial footage from broadcasters showed houses reduced to rubble and thick plumes of smoke rising from the hilly Saganoseki district of Oita city. 

The flames had also spread to nearby forested slopes and an uninhabited island more than one kilometre off the coast, likely due to strong winds, local media reported.

The blaze started on Tuesday evening and has burned 48,900 square metres- forcing 175 residents in the district, some 770 km (478 miles) southwest of Tokyo, to flee to an emergency shelter, Japan's Fire and Disaster Management Agency said.

The cause of the fire was under investigation, the agency added.

One person has been found dead, local media reported citing police sources, while a woman in her 50s was reported to be hospitalised for mild burns.

"I extend my heartfelt condolences to all residents who are evacuating in the cold," Japanese Prime Minister Sanae Takaichi said in a post on X.

The fire has caused power outages at around 300 houses in the district, according to Kyushu Electric Power.

The number of buildings and size of the area engulfed in flames make it the largest urban fire in Japan since a 1976 blaze in Sakata, excluding incidents caused by earthquakes. 

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