A 7.3 magnitude quake struck off Japan's east coast Saturday but no destructive widespread tsunami was expected, the Pacific Tsunami Warning Center said.

The quake struck at a depth of 10 kilometres (6.2 miles) at 3:10am local time (1710 GMT Friday), 320 kilometres southeast of Ishinomaki in Miyagi Prefecture, according to the US Geological Survey.

The USGS intially said its magnitude was 7.5, and issued a green alert on its website, signalling a low probability of deaths or economic losses.

Eastern Japan, a seismically active region, was struck by a 6.5 magnitude earthquake last month causing tremors to be felt 600 kilometres away in Tokyo.

More than 18,000 people died when a 9.0 magnitude sub-sea earthquake sent a towering tsunami barrelling into Japan's northeast coast in March 2011 in the country's worst post-World War II disaster.

Cooling systems at the Fukushima nuclear plant were knocked out, sending reactors into meltdown and forcing tens of thousands of people to flee.