So what do we know? Here's a run down of events so far:

- The biggest earthquake to hit Japan in 140 years struck the northeast coast on Friday, triggering a 10-metre tsunami that swept away everything in its path, including houses, cars and farm buildings on fire.

- The earthquake struck at 1446 local time (0546 GMT).

- 22 people are confirmed dead, with many more missing. Some news agencies are reporting a higher number of fatalities.

- The Philippines, Taiwan and Indonesia all issued tsunami alerts, reviving memories of the giant tsunami which struck Asia in 2004. The Pacific Tsunami Warning Centre issued alerts for countries to the west and across the Pacific as far away as Colombia and Peru.

- There were several strong aftershocks. In Tokyo, buildings shook violently. An oil refinery near the city was on fire, with dozens of storage tanks under threat.

- Stunning TV footage showed the tsunami carrying the debris and fires across a large swathe of coastal farmland near the city of Sendai, which has a population of one million. The pictures suggested the death toll was going to rise.

- Sendai is 300 km (180 miles) northeast of Tokyo and the epicentre at sea was not far away.

- Thick smoke was also pouring out of an industrial area in Yokohama's Isogo area. TV footage showed boats, cars and trucks floating in water after a small tsunami hit the town of Kamaichi in northern Japan. An overpass, location unknown, appeared to have collapsed into the water.

- UK airlines have cancelled flights to Tokyo.

- The western prefecture of Wakayama ordered 20,000 people to evacuate after further tsunami warnings.

- Passengers on a subway line in Tokyo screamed and grabbed other passengers' hands during the quake. The shaking was so bad it was hard to stand, said Reuters reporter Mariko Katsumura.

Even in a nation accustomed to tremors, the massive earthquake and the tsunami it triggered have been terrifyingly different, writes Chisa Fujioka.
uk.reuters.com

The countries for which a tsunami warning is in effect now includes: Russia, Taiwan, the Philippines, Indonesia, Papua New Guinea, Australia, New Zealand, Fiji, Mexico, Guatemala, El Salvador, Costa Rica, Nicaragua, Panama, Honduras, Chile, Ecuador, Colombia and Peru.

Some regions could be hit by waves within an hour, while for others it could be many hours.

Hirofumi Yokoyama, spokesman for Japan's meteorological agency, said in a briefing: "Historically, the magnitude scale was different, so simple comparison is not possible - but 8.8 is one of the largest we have experienced in Japan. It is the largest recorded by the equipment currently in place".]

Hidekatsu Hata, manager of a noodle restaurant in Tokyo's Akasaka area, told Reuters of the moment the earthquake struck. "I was terrified and I'm still frightened," he said, "I've never experienced such a big quake before."

The West Coast and Alaska Tsunami Warning Center has issued a warning for: the coastal areas of California and Oregon from Point Concepcion, California to the Oregon-Washington border; the coastal areas of Alaska from Amchitka Pass, Alaska (125 miles W of Adak) to Attu, Alaska; the coastal areas of California from the California-Mexico border to Point Concepcion, California; and the coastal areas of Washington, British Columbia and Alaska from the Oregon-Washington border to Amchitka Pass, Alaska (125 miles W of Adak).

Some amateur footage reportedly captured in Sendai when the earthquake struck.

Map from U.S. Geological Survey showing earthquake activity in Japan in recent days: earthquake.usgs.gov

Apologies, the amateur video we posted earlier purporting to show the Japan earthquake was actually shot in Christchurch. Thanks @gary for pointing that out.

The Australian Government Bureau of Meteorology says: "There is no tsunami threat to the Australian mainland, islands or territories". www.bom.gov.au