A 6.9-magnitude earthquake struck northeastern Japan on Tuesday morning at about 6 AM local time (GMT 9 pm Monday), which triggered a minor tsunami wave.

The earthquake was initially approximated at 7.3 in magnitude, but later downgraded to 6.9 by US Geological Survey. Its epicenter was located off the coast of Fukushima prefecture in Honshu island at a depth of about 9 miles.

The height of waves triggered by the quake varied in different coastal regions, from 1.4 meters at Sedai port in Miyagi Prefecture to 60 cm at Onahama Port in Fukushima Prefecture. A one meter high tsunami wave hit the Fukushima Daiichi nuclear power plant which was struck by the massive tsunami in March 2011 sending its three reactors into meltdown at the time.

TEPCO plant operator said that there were no reports of damage to the Daiichi plant, but a cooling system at another Daini facility temporarily stopped working in an automatic response to the tsunami impact. It later resumed operation.

No major damages were reported from the quake, but tremors were felt as far as in Tokyo.

Residents of both the Fukushima and Miyagi Prefectures were asked to evacuate coastal areas in the morning, causing long traffic jams on the roads.

The government issued warnings on national broadcaster NHK, and sirens were sounded all over the eastern coastlines. NHK displayed a red message in large font "Flee immediately!" while the bottom of the screen said "Tsunami warning is in effect."

However, the warnings were scaled to non-threat levels after about four hours of the quake.

Witnesses said that the quake was strong and lasted for about a minute.

"It was huge and lasted so long. The tsunami siren warning can be heard from the coastline. The ground is still shaking. I'm so scared. But my concern is rather the situation at the nuclear plant," Akemi Anzai, resident of Minamisoma city north of the Fukushima plant, told AFP.

In the town of Iwaki, which is about 40 miles from Fukushima Daiichi nuclear plant, reported a fire at a petroleum refining facility but it was quickly brought under control.

Japan Railways suspended operation in eastern Japan to assess any damage caused by the earthquake on the tracks.