TOKYO, Japan -- Hundreds of people have been injured after the strongest earthquake so far this year shook the northern Japanese island of Hokkaido. The magnitude 8.0 quake hit at 4:50 a.m. (1950 GMT) Friday forcing the evacuation of 41,000 people and prompting authorities to issue tsunami warnings that extend as far as Hawaii. Another temblor of similar intensity struck just over an hour later and multiple aftershocks have been felt. Residents on the eastern side of Hokkaido were urged to evacuate. Several million people live on the island but no deaths had been reported. Japan's national broadcasting agency, NHK, reported 236 people had been hurt. CNN Tokyo Bureau Chief Rebecca MacKinnon said tsunami waves measuring about 3 feet (1 meter) had begun hitting the eastern coast of Japan's northernmost island, and officials warned all residents in the region to seek higher ground. Evacuees have been filling schools and public buildings at a safe distance from the sea as authorities are also warning of potential aftershocks over the next 24 hours. A fire broke out at oil refinery on the island after the earthquake, and television stations reported a train derailment and a landslide near a highway tunnel. Japanese authorities said the quake's epicenter was located 50 miles (80 kilometers) offshore, about 796 miles north/northwest of Tokyo. According to the U.S. Geological Survey, earthquakes with magnitudes of 4.5 or greater can be recorded by sensitive seismographs around the world. On average, there is one magnitude-8, or great, quake a year in the world, The Associated Press reported USGS geophysicist Brian Lassige as saying. The amount of energy released in a magnitude-8 earthquake is equivalent to that contained in 1.01 billion tons of TNT, according to the USGS. A tsunami watch has been issued for the U.S. state of Hawaii. "Based on all available data, a tsunami may have been generated by this earthquake that could be destructive on coastal areas even far from the epicenter," said the announcement from the National Tsunami Hazard Mitigation Program. Only six days ago a 5.5-magnitude quake shook Japan. The September 20 earthquake was centered nearly 870 kilometers (540 miles) south-southeast of Tokyo, near Japan's Bonin Islands, a remote volcanic island group in the Pacific Ocean. Seven women attending a memorial service at a Tokyo Buddhist temple were slightly injured when one of the temple's walls collapsed on top of them, officials said. Earlier this month, Japan marked the 80th anniversary of a magnitude 8.3 quake that devastated Tokyo and neighboring Yokohama, killing at least 140,000 people. In January 1995, a magnitude 7.2 temblor in Kobe killed more than 6,000 people. Also on Friday, a moderate earthquake shook northeastern Taiwan, the Central Weather Bureau said, but no damage or injuries were immediately reported. The 4.9-magnitude quake hit at 7:43 a.m.. Its epicenter was under the Pacific Ocean about 12 miles east of Nanao town, the weather bureau said.