A 7.4 magnitude earthquake off north-eastern Japan near Fukushima prefecture has prompted a tsunami advisory.

The quake struck on Tuesday morning at about 6:00 am local time (21:00 GMT, Monday), the Japan Meteorological Agency said.

The depth of the quake was estimated to be 30km (18.6 miles), the agency said.

The initial tsunami warning of possible 3m (10ft) waves was downgraded to an advisory just before 10:00 local time, reports BBC.

An advisory was also issued for Miyagi prefecture, where a 1.4m wave (4.6ft) was observed at Sendai port.

The US Geological Survey initially put the magnitude at 7.3 but later downgraded it to 6.9, lower than the number given by the Japanese authorities.

Cabinet Chief Secretary Yoshihide Suga told a televised news conference that the water cooling system on the third reactor of the Fukushima plant had stopped working, but there were no signs of damage and no other abnormalities at other nuclear facilities.

The plant operator later said it had restarted the cooling system, and reported only small temperature increases, within safety limits.

All reactors in the Fukushima nuclear plant were shut down following the 2011 disaster, but cooling is still needed for the used nuclear fuel stored on the site.

Damage from the quake remains unclear, but there are some reports of minor injuries. Tremors were felt in Tokyo and residents were urged to evacuate some coastal areas.

Ships could be seen moving away from harbours in Fukushima prefecture, and car manufacturer Nissan suspended work at its Fukushima engine factory.

BDST: 0921 HRS, NOV 22, 2016
AP/SR