A powerful 7.4 – magnitude earthquake hit northeastern Japan late on April 7, seismologists said, promoting Japanese authorities to issue a localised tsunami alert.

The quake, which hit at 11:32pm local time, had a magnitude of 7.4, according to the US Geological Survey (USGS), which said it struck 66km east of Sendai .

Japan ’s weather bureau issued a tsunami alert for the Pacific coast, saying that waves of up to two metres could hit the shoreline.

In a statement on its website the Hawaii-based Pacific Tsunami Warning Centre said it did not expect a Pacific-wide tsunami.

The quake had a depth of 25.6km, the USGS said.

Meanwhile, workers at Japan ’s stricken nuclear plant on April 7 pumped nitrogen into a cripped reactor in a bid to prevent a possible explosion and contain the world’s worst atomic accident for 25 years.

With the crisis at the Fukushima Daiichi plant approaching the end of its fourth week, operator Tokyo Electric Power (TEPCO) said it was concerned a build-up of hydrogen gas at the No.1 reactor could cause another explosion at the site.

Workers began pumping in nitrogen, an inert gas abundant in the atmosphere, which they hope will displace the oxygen. The process to inject 6,000 cu.m will take around six days, TEPCO said.

TEPCO said it was also planning to inject nitrogen gas into reactors No 2 and 3 as a protective measure./.