The number of people who have died after a powerful earthquake hit southwestern Japan has risen to 34, authorities in Kumamoto prefecture said on Thursday.

Rescuers are still working to find survivors after the magnitude 6.8 earthquake hit Kumamoto prefecture on Kyushu island on Tuesday, causing widespread damage to houses and power lines.

Several people died after part of a shopping centre collapsed and an explosion ripped through the mall about an hour later.

Thousands of displaced residents are now staying in evacuation centres – though the challenge is to keep them cool and hydrated as the region battles sweltering heat.

Temperatures could reach 39C in the prefecture in the coming days, according to forecasts, with officials urging survivors and rescuers to take precautions against heatstroke.

On Wednesday, Japan’s defence minister Shinjiro Koizumi announced the delivery of 300 air conditioners to Kumamoto, with 150 of the units bound for evacuation centres.

Around 9,000 displaced residents have been put up in evacuation centres, and more than 30,000 households were out of power as of Wednesday.

Yukiya Sanoue, who works at one of the centres, told the BBC that heat stroke was the biggest concern at his facility, which hosts about 1,000 people. About 30% of the people at his evacuation centre are senior citizens.

He said their electricity and water supplies had stopped since the earthquake, and the centre had been without air conditioning until Wednesday afternoon when they received a generator.

Quite a few people are suffering from conditions similar to heatstroke, and several have been taken to hospital, he said.

More than 100 aftershocks have been recorded since the initial quake, and many have taken to sleeping in their cars for fear of further tremors.