Army troops and other rescuers rushed Saturday to save scores of trapped residents on the southern island of Kyushu in Japan, following a magnitude 7.3 earthquake that shook the Kumamoto region early on the same day - killing at least 32 people.

The quake triggered a tsunami advisory which was later lifted, according to a senior government official.

The earthquake on Saturday followed a 6.4 magnitude quake on Thursday that killed nine people in the area.

Chief Cabinet Secretary Yoshihide Suga said that 1,500 people had been injured in the quakes and more than 91,000 had been evacuated from their homes. More than 200 homes and other buildings were either destroyed or damaged, she added on Saturday.

Japanese Prime Minister Shinzo Abe voiced concern over possible secondary disasters due to inclement weather.

"The wind is expected to pick up and rain will likely get heavier. Rescue operations at night will be extremely difficult," he told a government meeting on Saturday. "But there are people waiting for help. Please do your utmost while putting top priority on human lives."

'Fortunately, no tsunamis have been triggered'

The soil is already loosened by the earthquakes, so rainfalls could cause further mudslides. Landslides have already cut off roads and destroyed bridges in the Kumamoto region, slowing down rescue operations.

Police received reports of 97 cases of people trapped or buried under collapsed buildings, while ten people were caught in landslides in three municipalities in the region, Japan's Kyodo News agency reported on Saturday.

The Japan Meteorological Agency said the magnitude 7.3 earthquake early on Saturday may have been the main one and the one from Thursday night the precursor.

David Rothery, professor of planetary geosciences at The Open University in Britain, told AP the earthquake on Saturday morning was 30 times more powerful than the one on Thursday.

"It is unusual but not unprecedented for a larger and more damaging earthquake to follow what was taken to be the 'main event'," he explained on Saturday.

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

"Fortunately, this time the epicenters have been below land rather than under the sea, and no tsunamis have been triggered," Rothery said.

das/rc (AP, Reuters)