Tokyo ( CNN ) -- At least six people were killed when a magnitude-6.4 earthquake struck Japan Tuesday morning , a local fire department said . The six were killed when a landslide triggered by the quake buried three homes in Iwaki , the city 's fire department said . Three people were rescued and hospitalized , and fire officials were working to rescue an unknown number of others believed to be trapped , the department said . The quake struck at about 8:08 a.m. Tuesday ( 7:08 p.m. Monday ET ) , according to the U.S. Geological Survey . It had a depth of about 13 kilometers ( 8 miles ) and was centered about 77 miles east-southeast of Tokyo . Monday night , one person was killed in Iwaki and several others were trapped when a powerful 6.6-magnitude earthquake triggered landslides there , the fire department said . It happened exactly one month after the country 's devastating 9.0-magnitude quake and tsunami . Threat level now on par with Chernobyl . The earlier quake was centered about 100 miles ( 164 kilometers ) northeast of Tokyo and about 30 miles ( 50 kilometers ) southwest of the crippled Fukushima Daiichi nuclear plant , according to the U.S. Geological Survey . The landslides in Iwaki buried three houses . Police in Fukushima Prefecture initially reported that four people were trapped . The Iwaki Fire Department later said more than four people were trapped , but the exact number was unclear . Authorities were trying to rescue them . Their condition was not immediately known , police said . The earthquake did not cause a tsunami . Japan to evacuate more towns . Workers at Fukushima Daiichi nuclear plant , which has suffered cooling problems and radiation leaks since the March 11 earthquake and tsunami , evacuated briefly but soon returned to resume their efforts to cool the troubled facility . Prime Minister Naoto Kan delayed a scheduled news conference as a result of the earthquake , his office said . The government wants to handle the immediate emergency before holding a news conference , the office said . Japan to evacuate more towns . The Tokyo Electric Power Company said 220,000 households and businesses in Fukushima were without power after Monday 's quake . Japan has been hit with hundreds of aftershocks since the March 11 earthquake and ensuing tsunami that killed at least 13,116 people . More than 14,000 remain missing . CNN 's Junko Ogura contributed to this report .
NEW : three people were killed and 6.6-magnitude injured in Monday 's quake . It was centered about 77 miles east-southeast of Japan . Monday 's 6.6-magnitude quake triggers several landslides in Iwaki . The earlier quake prompted workers at the Fukushima plant to evacuate briefly .