Japan, which has been rattled by more than 150 aftershocks since Friday's devastating earthquake, was shaken Sunday by a strong tremblor that caused buildings in Tokyo to sway.

The earthquake hit off Japan's eastern coast, closer to Tokyo than the massive quake that hit Friday. The U.S. Geological Survey says the temblor had a magnitude of 6.2 -- about the strength of the earthquake that severely damaged Christchurch, NZ last month.

So far, there are no reports of injuries or damage.

Since Friday, Japan has been hit by hundreds of aftershocks, including more than two dozen greater than magnitude 6.

University of Calgary geology professor Melissa Giovanni says such aftershocks could affect the island nation for weeks more -- and perhaps even months.

"The Earth's crust is trying to regain the equilibrium that it lost by slipping in this earthquake. And when you break a region of this size – the fault length is estimated to be over 200 kilometres long -- it can last for months," she told CTV News Channel Saturday night.

The death toll from Friday's quake and resulting tsunami is still not clear, but officials are warning it could reach into the thousands. So far, 763 are confirmed dead, but it is expected that number will climb much higher as search and rescue crews reach the areas most affected.

Among some of the most worrying developments:

  • The fate of four trains lost during the disaster remains unclear
  • Officials have had no contact with about 10,000 residents of Minamisanriku, a town of some 17,000 people on Japan's north-east Pacific coast, according to Kyodo News agency
  • Police said they've found 200 to 300 bodies washed up on beaches, but are still assessing the extent of the devastation in Sendai and along the coast.

"Our estimates based on reported cases alone suggest that more than 1,000 people have lost their lives in the disaster," Japan's Chief Cabinet Secretary Yukio Edano said. "Unfortunately, the actual damage could far exceed that number considering the difficulty assessing the full extent of damage."

Images captured from the sky showed one hospital in Miyagi Prefecture, the region closest to the epicentre, surrounded by water. Staff had painted "SOS" on the building's rooftop, and could be seen waving white flags.

Devastation stretched hundreds of kilometres along the coast, where about 300,000 hungry survivors huddled in darkened emergency centres in five prefectures, cut off from rescuers, electricity and aid.

"All we have to eat are biscuits and rice balls," Noboru Uehara, 24, a delivery truck driver told the Associated Press. "I'm worried that we will run out of food."

Power and water in short supply

An estimated 5.57 million households were still without electricity on Saturday, while more than 1 million homes had their water supply cut off.

Some 3,400 buildings have been damaged or destroyed and 200 fires have been reported in the stricken area. Officials said 181 welfare facilities, including nursing homes, have been damaged.

Fires continued to burn in residential areas as further earthquakes and aftershocks, some registering upwards of magnitude six, continued to rattle the area.

Rescue workers dug through the rubble Saturday while military helicopters plucked survivors, stranded by floodwaters, from rooftops.

Phone reception was cut in stricken areas, while hundreds of people lined up outside the few still-operating supermarkets for basic necessities. The gas stations on streets not covered with water were packed with people waiting to fill their cars' gas tanks.

Japanese Prime Minister Naoto Kan said late Saturday evening, local time, that more than 3,000 people had been rescued.

"We will do our very best to rescue all survivors," Kan said to reporters upon touring the devastated area.

"We'd first like to focus on saving lives and secondly the comfort of the evacuees," he added. "There will be many resources that will be needed for this evacuation process."

Friday's 8.9 magnitude quake -- one of the biggest ever recorded -- and the resulting tsunami laid waste to whole sections of northern Japan.

Survivors who had fled the port city of Sendai were streaming back to the town Saturday, telling of seven-metre waves that swept cars, boats, homes and trees as far as 10 kilometres inland.

Missing trains and transit woes

In the immediate wake of the disaster rail operators lost contact with four trains running on coastal lines and still had not found them by Saturday afternoon local time according to Kyodo News agency. The East Japan Railway Co. said it did not know how many people were aboard.

The fate of the trains remains unclear, though there are reports of passengers and crew members being rescued.

Most buildings out of range of the tsunami appeared to have survived the quake without much damage, though some older wooden structures were toppled. Paved roads had buckled in some places.

Japan has sent some 50,000 soldiers into the area to assist with rescue efforts, recalling the search and rescue workers it sent to New Zealand in the wake of that country's recent quake. The U.S. on Saturday said one aircraft carrier bearing relief supplies is already in Japan, while another is on its way. Additional rescue teams from Australia, New Zealand, South Korea and the U.S. are also on their way, part of an effort coordinated by the United Nations.

Sniffer dogs, personnel and other help is also reportedly on its way from Singapore, Switzerland and the U.K.

With files from Associated Press