A strong earthquake with a preliminary magnitude of 6.1 rocked the Tokyo (search) area early Monday, but there were no immediate reports of injuries or damage.
The quake was centered northeast of Tokyo and was focused about 36 miles underground, the Meteorological Agency (search) said.
There were no immediate reports of damage or injuries, police in Chiba prefecture near the epicenter said.
The Meteorological Agency said there was no danger of the quake generating a tsunami (search).
Both runways at Tokyo's Narita international airport were temporarily shut down for about 15 minutes after the temblor, but had now resumed operations, said airport spokesman Koitsu Ito. Local media reported temporary train delays as well.
Kyodo News agency said there was no damage to a nuclear facility in nearby Ibaraki prefecture.
A magnitude 6 earthquake can inflict widespread damage in a populated area. Last October, Japan suffered its deadliest quake in a decade when a magnitude 6.8 tremor rocked the northern Japanese region of Niigata, killing 40 people and injuring more than 2,700.
Japan, which rests atop several tectonic plates, is among the world's most earthquake-prone countries.