AN earthquake has struck off the east coast of Japan — just 320 kilometres east of Fukushima nuclear plant.

The tremor is said to have had a magnitude of 6.1, according to the US Geological Society (USGS).

Prelim M6.1 earthquake off the east coast of Honshu, Japan Sep-20 16:37 UTC, updates https://t.co/ewCuMgBAP0, 0 #quake tweets/min — USGSted (@USGSted) September 20, 2017

The American scientific agency, which tracks natural disasters around the world, said the quake happened 281 kilometres from Fukushima nuclear power plant.

The Japan Meteorological Agency said no tsunami warning was in effect and the USGS said only weak shaking would have been felt on Honshu and the risk of damage was likely to be minor.

Fewer than 40 reports of people feeling the quake were registered on the Geological Survey website.

It comes as Mexico is reeling from a magnitude-7.1 earthquake that collapsed buildings and killed at least 225 people.

Japan sits at the junction of four tectonic plates and experiences a number of relatively violent quakes every year.

But rigid building codes and strict enforcement of them mean even strong tremors typically do little damage.

A 15-metre tsunami sparked by an earthquake in the Pacific caused the Fukushima nuclear disaster in 2011, leaving 18,000 dead or missing.

The plant’s power supply was disabled during the catastrophe, preventing the cooling of the nuclear reactors and causing one of them to stop working.

Nearly 500,000 people fled the area and a 20-kilometre exclusion zone was set up.