A strong earthquake tremor has shaken northern Japan, four days after a quake that killed at least 31 people.
The prime minister visited the region just the day before
The magnitude 6.0 tremor hit at about 1040 (0140 GMT). No injuries or fires have been reported so far but a large building reportedly collapsed.
The quake was centred on Hirokami, Niigata prefecture - the same region most badly affected by Saturday's quake and aftershocks.
The tremor was also felt in Tokyo where tall buildings shook.
The most powerful of Saturday's tremors, which have become Japan's deadliest in a decade, measured magnitude 6.8.
Local hospitals have said they are overwhelmed by the more than 2,000 injured on Saturday. More than 100,000 people have been staying in emergency shelters, too scared by aftershocks to return home.
TV pictures from the shelters showed people throwing themselves to the floor and screaming in terror as the tremor struck on Wednesday morning.
"Aftershocks are continuing - we don't know what the
damage situation is yet," AP agency quoted Kazumasa Sakurai, an official at the Hirokami city hall, as saying.
Train and air services have been suspended, but a nearby nuclear plant is
functioning normally, local TV reported.
A building fell down in Ojiya, a town badly hit on Saturday, reported Reuters.
The Japanese Prime Minister Junichiro Koizumi visited Niigata, 260km (160 miles) north of Tokyo, on Tuesday.
"I've again been made keenly aware of the need to put together response measures for both the national and local governments," he said.
Bad weather conditions - continuing rain and temperatures set to drop below freezing - have contributed to the suffering.
But 76-year-old Kazuo Hotaka, staying at a school gymnasium in Nagaoka, in Nagaoka prefecture, said he was not succumbing to the cold.
"We don't have time to get sick. There's too much to do, too much to worry about, and too little information," he told Reuters.
Rescuers were still looking for three people missing after Saturday's quakes, the largest of which was of magnitude 6.8.
They are a woman and her two small children who were driving home on Saturday after visiting a friend in the city of Niigata.
Authorities warned there is a desperate need for food and water supplies.
The earthquakes follow a record 10 typhoons to hit Japan this year, including one that killed at least 80 people last week.