A major aftershock has rattled Japan, exactly one month after a earthquake and tsunami devastated much of the country's northeast.
The 7.1-magnitude tremor happened at 5.16pm on Monday with a depth of just 10km and centred 22km southwest of Iwaki in Fukushima prefecture.
A tsunami alert is in place for parts of the country, while buildings shook in the capital Tokyo.
There have been several large tremors after a 9.0-magnitude quake triggered a tsunami that devastated much of the north-east on 11 March and crippled the Fukushima Daiichi nuclear plant.
Japan's meteorological agency issued a tsunami warning for parts of the northeast coast, saying a one-metre wave could hit Ibaraki prefecture. A 50cm wave was expected in Fukushima prefecture, AFP reports.
Workers battling to contain the crisis at the stricken nuclear plant were ordered to evacuate, plant operator Tokyo Electric Power Company said on Monday.
Officials say there have been no major irregularities but power was cut to the crippled reactors.
Earlier on Monday, people fell silent at 2.46pm to mark one month since the disaster. Almost 28,000 people are dead or missing, while thousands more remain in shelters.
Prime Minister Naoto Kan thanked people around the world for their support. In an open letter placed in several newspapers, he said that the support had brought hope and inspired courage at a desperate time.
Evacuation zone expanded
Japan on Monday expanded the evacuation zone around the Fukushima nuclear plant due to high levels of accumulated radiation in the area.
Chief Cabinet Secretary Yukio Edano said villages and towns outside the 20km evacuation zone that have had more accumulated radiation would be evacuated.
Children, pregnant women and hospitalised patients should stay out of some areas 20km to 30km from the plant, he said.
Japan had refused to extend the zone despite international concerns over radiation spreading from the six damaged reactors at the Fukushima plant which engineers are still struggling to bring under control after they were wrecked by the 15-metre tsunami, Reuters reports.
Engineers at the damaged plant said on Sunday they were no closer to restoring the plant's cooling system, which is critical if overheated fuel rods are to be cooled and the reactors brought under control.
They hoped to stop pumping radioactive water into the Pacific Ocean on Monday, days later than planned.
The International Atomic Energy Agency has urged Japan to extend the zone and some countries, including the United States, have advised their citizens to stay 80km away from the plant.
