A painstaking search through tonnes of mud and splintered houses entered its second night Thursday on a typhoon-battered Japanese island, where the death toll from landslides rose to 21.

Hundreds of police, firefighters and troops searched for the more than 30 people still missing in an area where buildings were swallowed when a mountainside collapsed.

Typhoon Wipha, dubbed the strongest in a decade, never actually made landfall as it surged past Japan, but violent winds and torrential rain set off mudslides that buried neighbourhoods on Oshima.

At least 21 people died and 33 were still missing on the island, which lies 120 kilometres (75 miles) south of the Japanese capital, broadcaster NHK said.

One woman also died in western Tokyo, police have said.

On Oshima, about 15 police officers spent the morning using chainsaws and shovels to free the body of an elderly woman buried in mud and the smashed remains of a wooden building, an AFP reporter said.

The woman was formally pronounced dead later in the day.

Elsewhere troops, who arrived on the island on Wednesday morning just hours after it was raked by the storm, fanned out on paths up a mountainside shouting: "Is there anybody there?"

Spokesman Yoshinori Sano said the men were "hopeful" of finding survivors among the devastation.

"A total of 278 of us came yesterday, and we have been looking for survivors since then, without sleep or rest," he told AFP.

"We are searching every inch of the area to find survivors, there is still hope."

Resident Tadashi Sogi said his house had been swept 30 metres (yards), with much of it engulfed by the thick mud.

As he loaded his car with a few salvaged belongings -- including a photograph album -- he said he was going back to join the rescue effort.

"The lives of other people come before all these things," he said, gesturing to his soiled mementos.

As night fell, rescuers set up floodlights in areas where they thought people might be trapped, with teams expected to carry on the back-breaking search throughout the night.

Kyodo, citing a government source, reported Prime Minister Shinzo Abe was readying to visit the island where he would "oversee work to search for the missing, help surviving victims, and restore lifelines".

It gave no time for the visit.

Some of the roughly 8,000 people who live on the island had sought shelter in evacuation centres as the huge storm approached, reporting water gushing into their homes as it dumped more than 12 centimetres (5 inches) of rain on Oshima in an hour.

But criticism was growing Thursday of the island's mayor, Masafumi Kawashima, who did not issue an evacuation advisory despite repeated warnings from meteorologists about the size of the typhoon.

Kawashima, who was away at a conference when the storm hit, told reporters he regretted not having told people to seek safety.

"I'd feared issuing an evacuation advisory in the middle of heavy rains in the dark could lead to a secondary disaster. But in retrospect, I think that was naive," he said.

Most of Japan, including the densely populated capital, was spared the worst of the typhoon, although three other people were still officially missing in the greater Tokyo area.

They were two elementary schoolchildren who were believed to have been near a beach in Kanagawa prefecture, and a man in his 50s who had not been heard from since alerting authorities to a landslide near his house in Chiba prefecture.

Flights in and out of Tokyo were back to normal on Thursday, after about 400 cancellations on Wednesday affecting more than 60,000 passengers.