At least 23 people were injured after a powerful magnitude 7.5 earthquake struck off northern Japan late Monday and triggered a tsunami in Pacific coast communities, officials said. Authorities warned of possible aftershocks and an increased risk of a megaquake.The quake hit at about 11:15 p.m. in the Pacific Ocean, around 80 kilometres off the coast of Aomori, the northernmost prefecture on Honshu, and prompted a tsunami warning.The US Geological Survey reported second earthquake of magnitude 5.1 early on Tuesday, about 122 kilometres south of Honcho at a depth of 35 kilometres.

Tsunami warning lifted

The Japan Meteorological Agency issued a tsunami warning, with one wave hitting a port in the northern region of Aomori, where Misawa is located.Several more waves reached the coast, measuring up to 70 centimetres (two feet, four inches), JMA reported.Early Tuesday the agency lifted the tsunami warning, according to Kyodo news agency. JMA kept lower-grade advisories in effect for parts of northern Japan for several hours, but those, too, were evenutally cancelled.About 480 residents were sheltering at Hachinohe Air Base, and 18 defence helicopters were mobilised for damage assessment, Defence Minister Shinjiro Koizumi said. NHK reported about 200 passengers were stranded overnight at New Chitose Airport in Hokkaido.

Meteorological agency warns of aftershocks

The meteorological agency cautioned about possible aftershocks in the coming days and said there was a slight increase in the risk of a magnitude 8-level quake and tsunami along Japan’s northeastern coast from Chiba to Hokkaido. It urged residents in 182 municipalities to monitor their emergency preparedness over the next week.

Witnes accounts

“I’ve never experienced such a big shaking,” convenience store owner Nobuo Yamada told the public broadcaster NHK in the Aomori prefecture town of Hachinohe, adding that “luckily” power lines were still operating in his area.Satoshi Kato, vice principal of a public high school in Hachinohe, told NHK he was at home when the quake struck and watched glasses and bowls fall and smash into shards on the floor. He drove to the school, designated as an evacuation centre, and encountered traffic jams and accidents as panicked people fled. “Nobody had yet come to the school to take shelter,” he said.Prime Minister Sanae Takaichi said in brief comments to reporters that the govt set up an emergency task force to urgently assess the extent of damage. “We are putting people’s lives first and doing everything we can,” she said.Later, she urged residents in the region to pay attention to the latest information from local municipalities. “Please be prepared so you can immediately evacuate as soon as you feel a tremor.”The quake struck about 80 kilometres northeast of Hachinohe, at a depth of about 50 kilometres below the sea surface. It occurred near the same area that suffered a magnitude 9.0 quake and tsunami in 2011 that killed nearly 20 000 people and destroyed the Fukushima Daiichi nuclear power plant.(Inputs from agencies)