By Joseph Campbell, Kaori Kaneko and Mariko Katsumura

âEven now, there are people waiting to be rescued, and this is a race against time. We will marshal all available resources on the ground to save and rescue as many people as possible,â Takaichi told reporters at her office in Tokyo a day after the quake struck, raising the toll from three deaths reported earlier.

The quake knocked out power to thousands of homes and ruptured roads across the region.

Rescuers pulled eight people from the rubble of a partially collapsed shopping mall early on Wednesday. Two women in their 20s were killed as an apparent explosion of unknown origin ripped the mall apart about an hour after the earthquake.

Authorities are investigating a possible gas explosion, local media reported.

Emergency fire rescue teams, police and army personnel were focusing on areas of the building where calls for help had been received.

The full extent of the disaster remained unclear.

Around 20 to 30 mall workers were unaccounted for on Tuesday, public broadcaster NHK said. Seven people are also missing after a chimney collapsed at a Nippon Paper Industries 3836.T factory, while four others are seriously injured, a local government official said. Hospitals were reported to be treating dozens of patients.

Across the prefecture, which also suffered a deadly earthquake a decade ago, around 260,000 people were instructed to go to evacuation centres, authorities said.

The quakeâs epicentre was about 20 kilometres (12 miles) south of Kumamoto City, central Kyushuâs largest city with a population of around 700,000.

Authorities have warned residents in the areas that felt the biggest tremors to be on alert for further strong quakes for about a week, as well as for the risk of landslides.

With more than 36,000 homes still without power, authorities are worried about the risk of heat stroke as temperatures soar to around 34 degrees Celsius (93 degrees Fahrenheit) on Wednesday.

SOME HOSPITALS OVERSTRETCHED

One hospital in Uki city, near the epicentre, said a power outage caused by the earthquake meant it was unable to function.

âItâs become like a field hospital,â the head of the administrative department told NHK. Another hospital in the city said it had suspended admissions as it could no longer handle additional emergency cases after accepting 86 injured people following the quake, including three with serious injuries.

Several passengers aboard high-speed trains at the time of the quake were also injured, operators said.

But it was the Aeon mall 8267.T, the largest in the prefecture, that was the most eye-catching disaster.

One side of the mall, which houses around 200 stores, was torn away in the blast, exposing steel beams and strewing debris across a parking lot, footage showed.

A spokesperson for mall operator Aeon 8267.T said customers and employees were evacuated right after the initial quake and that the exact cause of the ensuing explosion was unclear.

Aeon shares fell 1.9% in early trading in Tokyo. The benchmark index .N225 was up 0.8%.

Some major companies with plants in the area including Tokyo Electron 8035.T, a semiconductor equipment maker, and Honda 7267.T said they would suspend operations at their plants through Wednesday.

TSMC 2330.TW, the worldâs largest contract chipmaker, evacuated workers from its local plant as a precaution after the quake but said it had begun resuming operations late on Tuesday.

Some roads were also badly damaged, with large cracks splintering major highways and snarling traffic on Tuesday evening.

Located on the âRing of Fireâ of volcanoes and oceanic trenches partly encircling the Pacific Basin, Japan accounts for about 20% of the worldâs earthquakes of magnitude 6.0 or more.

A massive earthquake in Kumamoto 10 years ago killed 275 people and injured a further 2,739, according to an official count, and damaged thousands of buildings including the walls of the cityâs castle, a top tourist site.

(Reporting by Joseph Campbell in Kumamoto, Kaori Kaneko and Mariko Katsumura in Tokyo; Writing by John Geddie; Editing by Stephen Coates)