ASAKURA, Japan (Reuters) - Torrential rains battered southwestern Japan for a second day on Thursday, killing three people, with 100,000 ordered to evacuate their homes and while thousands of rescuers, some in helicopters, searched for survivors.

Parts of Fukuoka prefecture, on the island of Kyushu, were hit by 556 mm (22 inches) of rain in the 40 hours to 4 p.m. (0700 GMT) on Thursday, about 1.6 times the amount that usually falls in the whole of July, the weather agency said.

Television showed a military helicopter airlifting a stranded resident to safety and houses half submerged in murky water or destroyed by landslides.

“I heard this tremendous rumbling noise and then the house exploded. A tree burst through the wall into the room,” a sodden, dishevelled man told public broadcaster NHK after his house was hit by a landslide.

Three people had been killed, three were in “cardiopulmonary arrest” and eight were injured, NHK reported, while about 300 people were stranded, mostly in their homes, cut off by floods or landslides.

Thousands of soldiers, police and fire fighters fanned out, wading through water and plodding through mud to search for victims.

“Since daybreak today, we have mobilised 7,800 people from police, fire authorities and the Self-Defence Forces to do our utmost in searching and rescuing the affected,” Chief Cabinet Secretary Yoshihide Suga told a news conference.

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About 250 people had been rescued, but there were some areas where the rescue teams had yet to reach, he said.

The weather agency downgraded a special warning issued on Wednesday to Fukuoka and neighbouring Oita prefecture to a regular alert, but heavy rain was likely continue into Friday.

“Soil has been loosened in these regions because of the heavy rain ... Strict vigilance should be maintained,” an agency official told reporters.

Fukuoka and Oita prefectures are both largely rural.

The rain was caused by a low pressure area over the Pacific that fed warm, moist air into Japan’s seasonal rainy front.

Television footage showed a railway line left broken and twisted and roads eaten away by floods.

All operations stopped at a Daihatsu Motor Co plant in Oita because staff and parts could not get to the plant. The company also cancelled a shift at a plant in nearby Fukuoka.

A spokesman for JXTG Nippon Oil & Energy Corp said there was no impact on its Oita refinery operations and Toshiba Corp said its semiconductor plant in Oita was operating normally.