A moderate earthquake has hit Tokyo, waking residents and shaking buildings in the Japanese capital, but there has been no immediate report of damage.
At least 11 people received minor injuries in the capital in connection with the jolt on Saturday morning, but officials from the Tokyo Fire Department say no one was seriously injured.
The 5.4-magnitude quake, with its epicentre located in Tokyo Bay, struck at 5:49am local time, according to the US Geological Survey.
The Japan Meteorological Agency said no tsunami warning had been issued, and that the quake was 70 kilometres deep.
But the agency warned sizeable aftershocks could strike in Tokyo at least in a few days, and called on residents to stay vigilant against possible landslides following heavy rain that hit the region earlier this week.
Authorities have been grappling with the aftermath of massive flooding that killed at least three people, as thousands of rescuers search for almost two dozen still missing in disaster-struck Joso city, which lies about 60 kilometres outside Tokyo.
Residents said the quake was not strong enough to knock many things from shelves, while at least five people were temporarily trapped in elevators, Japan's public broadcaster NHK said.
It also temporarily stopped Tokyo subways and trains, but service was quickly resumed.
The tremor did not cause any damage to the region's nuclear facilities, according to the government, and did not affect the areas that host the crippled Fukushima Daiichi nuclear plant, which went through meltdowns after a 9.0-magnitude quake and tsunami disaster in 2011.
It served as a reminder that a huge earthquake could strike the Japanese capital - which has a population of about 13 million people - at any time.