The gaping hole, around 20 metres (66 feet) by 15, exposed support columns of nearby buildings at a traffic intersection in the southern city of Fukuoka, prompting fears of further collapses.
TV footage showed two separate holes steadily expanding as they sucked in asphalt and soil in front of the city's Hakata Station, some time after 5am (2000 GMT Monday).
"It was a bit dark outside, and my first impression was, 'Is the road really falling?'" a young man who saw the sinkhole form told public broadcaster NHK.
"When I saw it, two holes were already there, and they continued to grow bigger.
"I got scared the most when a traffic light fell at an intersection close to where I was standing. I felt, 'I have to get out of here,'" he told NHK.
The hole continued to expand and by mid morning was around two storeys deep, and filling with water from broken pipes.
Fukuoka's transport bureau said the ongoing extension to a nearby subway line could be related to the creation of the sinkhole.
Fukuoka is the biggest city on the southernmost main Japanese island of Kyushu.
Its railway station is a major intersection, including for the superfast bullet trains that criss-cross the country.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)