Typhoon Lan, classified as an intense Category 4 storm by the Tropical Storm Risk monitoring site, was south of Japan and moving northeast at 40 kph on Sunday afternoon, the Japan Meteorological Agency (JMA) said.
An agency official told a news conference that while Lan appeared to have weakened slightly from its peak, it was still a powerful storm that could pound parts of Japan with more than 80 mm (3 inches) of rain an hour. It may make landfall near Tokyo early on Monday.
"It will make landfall as a strong typhoon," he said.
"The wind and rain will grow stronger as the night goes on, so take measures as needed as early as possible, preferably before it gets dark."
Wind gusts of up to 162 kph (100 mph) were possible across central and eastern Japan early on Monday, the JMA added.
The agency issued warnings for heavy rain and flooding on the Pacific side of Japan including the Tokyo metropolitan area, even though the typhoon is likely to be downgraded to Category 3 by Sunday evening, with the activity of a seasonal rain front intensified by the storm.
More than 70,000 households in various parts of Japan were advised to evacuate, with more than 5,000 ordered to do so, NHK public television said.
"I live alone and at night it's scary, so I came here as early as I could," one elderly woman told NHK at a evacuation centre in western Japan.
Several small landslides had occurred and rivers were rising dangerously close to the top of their banks in several parts of the country.
Prime Minister Shinzo Abe told reporters he had called on the government to take steps as early as possible to minimise any threats to people's lives.
More than 300 flights were cancelled and rail services were interrupted in southern and western parts of the country. By evening, wind and rain were intensifying in Tokyo.
Toyota Motor Corp said it was cancelling the first shift at all of its assembly plants around the nation.
The bad weather could hinder voter turnout in the general election, where Abe's Liberal Democratic Party-led (LDP) coalition is on track to roughly match the two-thirds "super majority" it held in parliament's lower house before dissolution.
Authorities in Okinawa moved the voting date to Saturday for some remote islands as the storm neared.
(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)