Manhole covers in Itabashi Ward, Tokyo, were blown free Thursday morning and methane gas and hydrogen sulfide were released from sewage pipes, officials said.
No one was injured in the incident.
At around 7:45 a.m., the 80-kg cover of a manhole popped up on a busy street in the Maeno district. The street surface then caved in, causing methane gas to leak from an underground sewage pipe, Tokyo Metropolitan Government officials said.
Manhole covers about a kilometer away were also lifted.
The Tokyo Fire Department said hydrogen sulfide, which is toxic, was also detected at the site.
Police officers urged residents to close their windows and keep their pets inside.
According to officials at the metropolitan government's waterworks bureau, an air cushion system, which adjusts sewage volume, may have broken down and led to an excessive buildup of pressure.
Manhole covers in the Maeno district last popped in August, officials said, adding they are looking into the cause of the incidents further.
A 46-year-old resident recalled hearing a rumbling sound and opening her window to the sight of vapor blasting several meters into the air.
"An odor like that of rotten vegetables wafted in the air for a while," she said. "It smelled so bad I could barely stay at home."