CNN Wire Staff
Tokyo (CNN) - A powerful earthquake struck Japan on Thursday, triggering a tsunami warning for one prefecture and advisories in others.
The warning and advisories were lifted about 90 minutes later, the Japan Meteorological Agency said, but it left millions of Japanese rattled.
The quake was closer to the Japanese coast than last month's 9.0-magnitude quake.
There were no reports of casualties from anywhere in the earthquake zone, though 20 people were injured, the National Police Agency said. Three of the 20 were thought to have serious injuries, said police.
The Japan Meteorological Agency said the quake was a magnitude 7.4. The U.S. Geological Survey said it was 7.1. The USGS also said Thursday's quake could be considered an aftershock - making it the biggest one since the March 11 quake.
Workers evacuated the Fukushima Daiichi nuclear plant following the quake, the Tokyo Electric Power Company said. The company said it has communication with the plant and the power is still on there. There were no immediate reports of damage, it said.
The workers returned later and were assessing any impact, CNN's Kyung Lah reported Friday. About four million homes remained without power.
The quake's epicenter was off the coast of Miyagi in northeastern Japan, the Japan Meteorological Agency said.
The USGS said the quake was centered 41 miles (66 kilometers) from Sendai - one of the areas worst hit by last month's 9.0-magnitude quake - and 73 miles (118 kilometers) from Fukushima, where a crisis has been under way at the nuclear plant since last month's tsunami.
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