The collapse began at about 5am local time near Hakata Station, the busiest in Fukuoka city in the southern island of Kyushu.
By afternoon, the hole was 30 metres long and 15 meters deep - more than half the size of an Olympic swimming pool - swallowing an entire five-lane intersection.
Nobody was injured but several multi-storey commercial buildings teetered dangerously at the edge of the abyss as it grew.
“I saw a stoplight fall. It was really scary,” one man told Fuji TV.
Fukuoka sinkhole in Japan
Television footage showed burst water mains spewing muddy water into the hole, which city officials said was probably caused by subway construction in the city of 1.5 million.
Online services for some banks were disrupted and power outages briefly hit 800 households as well as Fukuoka International Airport, but there were no reports of flight delays.
“All pedestrians avoid this area,” a policeman with a loudhailer said. “We are checking for gas leaks, so please don’t light your cigarettes.”
A smaller sinkhole happened in Fukuoka in 2014 at another location of the subway construction.
“An accident like this is unheard of, one that should not have happened,” Fukuoka mayor Soichiro Takashima said.
“We must prevent secondary accidents, and will do our utmost to restore important infrastructure.”
