The first quake occurred at 10:06 am (0106 GMT) off the coast of Fukushima prefecture, 250 kilometers (155 miles) north of Tokyo, with its focus 30 kilometers below sea-level, a spokesman for the agency said.

A second quake followed in the same area at 10.21 am, centred 40 kilometers below sea-level.

The quakes set off a small tidal wave which reached the coast of Miyagi prefecture just north of Fukushima at 10.43 am, raising water levels 20 centimeters (eight inches) above normal wave peaks, the spokesman said.

Tremors from the first quake were felt across the whole of northern Japan from Hokkaido island to the Kanto region around Tokyo, Japan Broadcasting Corp. (NHK) said.

"We are flying helicopters over the areas where a strong tremor was registered, but have not seen any major damage," said a police spokesman in Miyagi, where the strongest tremors were felt.

Nearly 100 people were injured when a quake measuring 7.0 on the Richter scale rocked the same area on May 27 followed by a series of powerful aftershocks. It was not immediately clear if Friday's quake was related to the earlier seismic activity.

TERRA.WIRE