A total of 155 army personnel and 25 vehicles arrived in the coastal city of Itoigawa.
Aerial footage broadcast live on Japanese TV showed massive orange flames and thick grey smoke spewing out of buildings throughout much of the day in the city of Itoigawa in Niigata prefecture.
A total of 155 army personnel and 25 vehicles arrived in the coastal city in the afternoon after Niigata Governor Ryuichi Yoneyama requested aid.
The blaze started at 10:28 am (0128 GMT) at a Chinese restaurant, according to a Niigata prefectural official, and a total of at least 17 fire trucks were deployed in the area.
As daylight receded, the bright burning flames contrasted with the darkening sky, while embers smouldered in some of the gutted structures.
"We can still see fire and smoke rising in the area from city hall," Atsuhiro Kawanami, a city official, told AFP in the early evening.
He said efforts to put out the fire were continuing and officials were still assessing its scale.
About 140 houses and buildings were damaged and 65 residents evacuated their houses to an auditorium next to the city hall, while an evacuation advisory was given to 586 residents in the neighbourhood.
"This is an area that has both residential houses and shops," Kawanami said, "but the fire happened during the day, so we think that many, if not most, residents were away."
Itoigawa is located on the northen coast fronting the Sea of Japan (East Sea) and has a population of 44,510 people, according to its website.
The fire, which dominated media coverage in Japan, spread quickly as winds accelerated, according to public broadcaster NHK.
Constant winds, registered at 40 kilometres (25 miles) per hour at 6:00 pm (0900 GMT) remained a challenge as authorities sought to control the flames.
"This was an area that was crowded with wooden structures, which is a type of townscape prone for fire to spread quickly," Ai Sekizawa, professor at Tokyo University of Science and an expert on fire protection, told NHK.
"On top of that, there was a strong wind," he added.
"This creates a condition that, once a fire starts, it can spread quickly, while on the other hand the fire can become difficult to contain."
Residents voiced both fear and frustration.
"I went to a hospital, and when I came home, I couldn't even go near my house," said a 85-year-old woman who took shelter at the city facility, adding that she was worried.
"Sparks of fire flew around," a man in the neighbourhood told NHK.
"That's why far away buildings unexpectedly caught fire and it became large-scale. I've never seen something like this before."
Despite the size of the fire, just two people were injured, both women in their 40s.
One fell sick after inhaling smoke and a prefectural government employee fell and hit her head, according to the fire division official.