TOKYO, April 21, 2026 (BSS/AFP) - At least six people were reported injured on Tuesday, a day after a powerful quake rattled northern Japan, but there appeared to be no major damage from the tremor that also triggered tsunami waves up to 80 centimetres (31 inches).

However, the Japan Meteorological Agency (JMA) also warned of an increased risk of a megaquake -- a tremor with a magnitude of 8.0 or stronger -- hours after Monday's 7.7 magnitude quake in Pacific waters off northern Iwate prefecture.

The jolt was so intense that it shook large buildings in the capital Tokyo, hundreds of kilometres from the epicentre.

Six people were reported injured by 8:00 am (2300 GMT Monday), two seriously, the Fire and Disaster Management Agency (FDMA) said in a statement.

There were no reported fire outbreaks or damage to important facilities, it said.

Japan issued a warning for tsunami waves of up to three metres (10 feet) but it was lifted hours after an 80-centimetre (31-inch) wave hit a port in Kuji in Iwate, one among a series of small waves that hit elsewhere in northern Japan.

The JMA said that "the likelihood of a new, huge earthquake occurring is relatively higher than during normal times".

Municipalities in the affected region issued non-compulsory evacuation directives to more than 182,000 residents, the FDMA said.

Japan is one of the world's most seismically active countries, sitting on top of four major tectonic plates along the western edge of the Pacific "Ring of Fire".

The archipelago, home to around 125 million people, typically experiences around 1,500 jolts every year and accounts for about 18 percent of the world's earthquakes.

The vast majority are mild, although the damage they cause varies according to their location and the depth below the Earth's surface at which they strike.

Japan is haunted by the memory of a massive 9.0 magnitude undersea quake in 2011, which triggered a tsunami that killed or left missing around 18,500 people and caused a devastating meltdown at the Fukushima nuclear plant.