Japanese authorities lifted the tsunami warning shortly after people were ordered to leave coastal areas [Reuters]

Japan was rattled by a magnitude-7.1 aftershock nearly a month after a devastating earthquake and tsunami flattened the northeastern coast.

Thursday's aftershock, the strongest since the day of the magnitude-9.0 quake, was a fresh blow to victims of that March 11 quake and subsequent tsunami that killed at least 25,000 people, tore apart hundreds of thousands of homes and sparked the ongoing crisis at a nuclear power plant.

Al Jazeera's Marga Ortigas, reporting from Mizusawa in northeast Japan, said there were reports of injuries and gas leaks following the quake.

"Some traintracks have also been displaced and people were trapped in lifts. But Japanese have said that they do not expect further damage."

The Japan meteorological agency briefly issued another tsunami warning, but later cancelled it.

Al Jazeera's Harry Fawcett, also reporting from Misuzawa, said a 50cm wave was observed, according to local media.

"That was not confirmed by officials. The tsunami warning has been lifted but it was of course extremely disturbing for people who recently went through the trauma of that huge tsunami on March 11."

Officials at the tsunami-ravaged Fukushima Daiichi nuclear plant said there was no immediate sign of new problems caused by the aftershock.

Japan's nuclear safety agency said workers there had retreated to a quake-resistant shelter in the complex. No one there was injured.

Officials said Thursday's aftershock hit 50km under the water and off the coast of Miyagi prefecture.

The quake struck at 11:32pm local time and initially measured 7.4 on the Richter Scale, however, the US Geological Survey in Golden, Colorado, later downgraded it to 7.1. Buildings as far away as Tokyo shook for about a minute.

In Ichinoseki, inland from Japan's eastern coast, buildings shook violently, knocking items from shelves and toppling furniture, but there was no heavy damage to the buildings themselves.

Immediately after the quake, all power was cut. The city went dark, but cars drove around normally and people assembled in the streets despite the late hour.

Paul Caruso, a geophysicist at USGS, said it struck at about the same location and depth as last month's huge quake.

It was the strongest of the more than 1,000 aftershocks that have been felt since, except for a 7.9 on the same day.

Don Blakeman, another USGS geophysicist, said it was the strongest aftershock since March 11, although several aftershocks on that day were bigger.

The USGS said the aftershock struck off the eastern coast 65km from Sendai and 115km from Fukushima.

A Pacific Tsunami Warning Center evaluation of the quake said an oceanwide tsunami was not expected.

However, it noted quakes of that strength can cause waves that are destructive locally.

Source: Al Jazeera and agencies