A powerful aftershock has struck north-east Japan, a month after a violent quake led to a devastating¹ tsunami².

日本东北部地区遭受一场强烈余震，一个月前的大地震引发一场毁灭性的海啸。

Officials ordered mass evacuations and workers at the damaged Fukushima nuclear plant took shelter after the quake triggered a tsunami warning.

But the alert was lifted after 90 minutes and no damage was reported at the nuclear plant.

Emergency crews said two people died as an indirect result of the quake and about 100 more were injured.

A 63-year-old woman died when the tremor³ knocked out power in Yamagata prefecture（县，辖区） , shutting off her respirator（口罩，呼吸器） .

And a 79-year-old man in Miyagi prefecture died of shock.

'So scared'

The latest earthquake - at a depth of 49km (32 miles) - struck off Japan's north-east coast, close to the epicentre of the 11 March quake.

All seven of the workers at the crippled Fukushima Daiichi nuclear power station were safe, a spokesman for plant operator, Tepco, told a news conference in Tokyo.

"They have not been injured and they have all taken shelter in our seismic-resistant building," he said.

The workers are trying to keep the damaged reactors⁴ cool to stop further releases of radioactive material.

Thursday's quake struck at 2332 local time (1432 GMT) on Thursday, 118km (78 miles) north of Fukushima, 40km offshore⁵.

First reports said it had a magnitude of 7.4 but that was later revised to 7.1, according to the US Geological Survey (USGS).

Last month's earthquake had a magnitude of 9.0 and struck at 32km deep.

Thursday's quake struck at about the same location as the 11 March quake.

The quake was strong enough to shake buildings in Tokyo, 265km to the south.

"It started off with small shakes, then shook（摇动） bigger," Miri Gono in Tokyo told the BBC by e-mail.

"I was alone in my house with my brother and we were so scared... We took our bottles of water and hid under the table."

Japan's meteorological（气象的） agency issued tsunami warnings and advisories⁶ for a stretch of coast 420km long, from Aomori prefecture in the north to Ibaraki prefecture in central Japan, just north of Tokyo.

Hundreds of aftershocks have shaken north-eastern Japan in the wake of the earlier earthquake, but few have measured higher than 7.0.

About 28,000 people are dead or missing, and hundreds of thousands were left homeless after the tsunami which ripped through the region.