Tens of thousands of people forced from their homes by back-to-back earthquakes in southern Japan spent a wet and windy night in temporary shelters on Saturday night.

A magnitude 7.3 earthquake shook Kumamoto province on the southwestern island of Kyushu Saturday at 1:25 a.m. local time. It struck slightly more than 24 hours after a magnitude-6.5 tremor in the same area on Thursday.

At least 41 people were killed and about 1,500 injured in the two quakes, which collapsed houses, triggered mudslides and destroyed bridges and roads.

The government said more than 400,000 houses remained without running water and another 100,000 homes were without electricity.

Broadcaster NHK said about 240,000 had received orders to evacuate, including some people living near a dam, which it is feared may collapse.

Heavy rains threatened to cause further mudslides and slow rescue operations on Sunday.

'Race against time'

"The wind is expected to pick up and rain will likely get heavier," Prime Minister Shinzo Abe told a government meeting. "Rescue operations at night will be extremely difficult ... It's a race against time."

More than 20,000 army troops and rescuers have been deployed to set up tents and reach stranded residents. More police, firefighters and medics were also set to arrive.

Earlier Saturday, rescuers saved 10 students stuck in a collapsed university apartment building in the town of Minami. Dozens of people are believed to still be tramped under rubble.

Authorities said the island's nuclear power plants were undamaged.

In March 2011, a magnitude 7.2 earthquake in northern Japan was followed two days later by a magnitude 9.0 quake that caused a devastating tsunami, which in turn triggered nuclear meltdowns at Fukushima. Nearly 20,000 people were killed in the disaster.

cw/cmk (AP, Reuters)