Dozens were evacuated in a similar incident last week in Konan city
About 350 people have been evacuated from their homes in northern Japan after poisonous fumes were released by a man who committed suicide.
The evacuation took place in the city of Otaru on the island of Hokkaido in the early hours of Thursday morning.
The 24-year-old man died after mixing detergent and other chemicals to produce hydrogen sulphide, a toxic gas.
Police have urged web providers to ban sites publishing tips on how to make the gas, after a spate of such deaths.
Japan's public broadcaster, NHK, said last month that about 40 people had used the technique to kill themselves this year.
The young man is said to have died in Otaru shortly after midnight, local time, after mixing the noxious gas.
His 58-year-old mother was found unconscious nearby and is recovering in hospital, police said.
The gas also spread into the surrounding neighbourhood, prompting the evacuation of about 350 neighbours to a school playground, where they waited about two hours for the fumes to clear.
Just one week ago, some 100 people in Konan city, southern Japan, fled their homes after another suicide victim - a girl in her early teens - released the gas.
Hydrogen sulphide is colourless but smells like rotten eggs and is highly toxic. In high concentrations, it can lead to suffocation or brain damage, while smaller doses can cause a sore throat, nausea and irritated eyes.
The latest evacuation comes a day after Japan's National Police Agency urged internet service providers to block websites which publish instructions on how to mix the gas.
"There are many cases of suicide and they often harm people living nearby," the agency said in a letter to a number of groups representing internet providers, reported Reuters news agency.
Japan, which has population of 128 million, has one of the developed world's highest suicide rates.
At least 30,000 people have killed themselves every year since 1998, according to national statistics.
Japanese authorities have set a goal of cutting the country's high suicide rate, through counselling programmes and blocking websites that offer suicide tips.