TOKYO, July 16 (Xinhua) -- Two women were killed, over 200 people were injured in an earthquake with a magnitude of 6.8, which rocked Niigata prefecture of central western Japan and surrounding areas on Monday morning, local reports said.

    According to Kyodo News, two women died in Kashiwazaki in Niigata after being taken to a local hospital due to the 10:13 a.m.(0113 GMT) quake. Of over 200 people injured in Niigata and Naganoprefectures, more than 100 were taken to hospital in Kashiwazaki.

    The weather service issued a tsunami warning immediately after the quake and relieved it about an hour later. Around a dozen aftershocks were registered from 10:34 a.m. (0134 GMT) to 13:53 a.m. (0453 GMT) in Niigata, with magnitudes around 3 on the Richter scale, according to Japan Meteorological Agency.

    The epicenter of the quake was around 17 kilometers below seabed in waters off Niigata prefecture, the agency said. The agency, which revised the major quake from 6.6 to 6.8 magnitude later at noon, also said that a strong aftershock may occur within the week.

    Over 20 houses collapsed in Niigata prefecture, local reports said. An electric transformer caught fire at the No. 3 reactor of Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear plant. The fire was brought under control around noon, local reports said. Other three reactors at Kashiwazaki-Kariwa nuclear plant automatically shut down. No radioactive leakage has been detected so far.

    The quake also caused power failures in over 21,700 houses in Niigata as of 11:00 a.m. (0200 GMT).

    East Japan Railway Co. said it halted bullet train services on the Tohoku, Joetsu and Nagano Shinkansen lines as well as other train services. The Tohoku and Nagano Shinkansen lines later resumed operations.

    Several parts of highway in Niigata were also closed after the quake. Niigata airport shut down its runways immediately after the quake to check for damage, airport officials said.

    The government has set up an emergency management center to handle the quake. Prime Minister Shinzo Abe, who has been in Kyushu of southern Japan, is on his way back to Tokyo due to the quake, local reports said.

    The quake measured upper 6 on the Japanese seismic intensity scale of 7 in Kashiwazaki and Kariwa in Niigata and Iizuna in Nagano, lower 6 in Joetsu and Nagaoka in Niigata, and upper 5 in Iiyama in Nagano. The earthquake also affected nearby prefectures including Ishikawa, Yamagata, Tochigi, Saitama, Fukushima and others.

    In October 2004, a major earthquake hit Niigata prefecture, killing 67 people and injuring over 4,800.