Prime Minister Naoto Kan has said Japan is experiencing its greatest hardships since World War II as it tackles the aftermath of an earthquake, tsunami and a growing nuclear crisis.

He said the situation at the quake-hit Fukushima nuclear plant remained grave, a day after an explosion at a reactor. Japanese broadcaster NHK says the total number of confirmed deaths caused by the disaster now stands at 1,351. But police warn that the death toll in Miyagi region alone could top 10,000.

Millions of survivors remain without electricity and authorities are stepping up relief efforts as the scale of the tragedy becomes clearer. About 310,000 people have been evacuated to emergency shelters, NHK says.

FAQ : The Science Behind Japan’s Quake and Tsunami

On Friday afternoon in Japan, disaster struck as a massive 8.9 magnitude earthquake generated a wall of water that surged over the east coast of the island nation, sweeping many to their deaths.

Here's what you need to know about the quake and its aftermath:

Where did the Japan earthquake come from?

Japan is situated along the world's most active earthquake belt, the Pacific Ring of Fire, where rigid plates in the Earth's crust collide along the rim of the Pacific Ocean. This earthquake originated 231 miles (373 kilometers) northeast of Tokyo and 80 miles (130 km) east of Sendai, Honshu in the Pacific Ocean. The earthquake occurred at a depth of about 15.2 miles (24.4 kilometers).

In this area, the Pacific Plate, the plate beneath the Pacific Ocean, is moving almost due west and being pushed down into the Earth's interior along a trench off Japan's east coast. On average, the Pacific Plate is moving at 3.5 inches (8.9 centimeters) per year, but this process is not continuous, according to Keith Sverdrup, a professor of geophysics at the University of Wisconsin-Madison. [The Science behind Japan's Deadly Earthquake]

Movement may stop as the plates stick together for a period and energy will build up, so when the movement does finally occur, it is much more dramatic, Sverdrup said. 

The process of one plate being pushed beneath another is called subduction, and it occurs all along the Ring of Fire, producing other earthquakes, including the 7.7 magnitude quake that struck off the coast of Indonesia in October.

How does the Japan earthquake rank in global records?

While the magnitude estimate of this latest earthquake may later be revised, 8.9 is the largest Japanese quake on record and the fifth-largest quake worldwide since 1900, according to the U.S. Geological Survey (USGS).

How did the Japan earthquake create a tsunami?

The earthquake caused the seafloor at the fault to suddenly shift vertically and this motion, in turn, shifted the water column above it. This motion then spawned a series of massive waves known as a tsunami. [Tsunami Hits Japan after Massive 8.9 Earthquake]

"It is not unlike dropping a pebble into a pond and seeing the ripple move," Sverdrup told LiveScience.com. The waves simultaneously spread toward the east coast of Japan and toward the west, on a much longer path to the west coast of North America.

"Last night, Japan's tsunami was at a location at which we have had giant tsunamis in the past," said Harry Yeh, a professor at Oregon State University who was born in Japan. In 1896 and 1933, tsunamis hit in the same area.

Yeh said his family in Tokyo is fine. "My father is 91 years old and he and my 92-year-old mother were taking a walk, and walking around they felt some kind of ground shaking," he said. "He thought he had a stroke."

Yeh is an expert on ocean and coastal wave dynamics, including tsunamis.

"A tsunami is really an intriguing phenomenon because it rarely happens," he said. The wave itself is unique, resembling neither a storm wave nor a long, tidal wave, and it alters both the ecology and the terrain of the land it touches. Watching the footage on TV, he said he was struck by how the speed of the water surging over fields and homes resembled that of a flooded river.

The highest of the waves are believed to have reached 30 feet (9.1 meters).

How well can we predict earthquakes and tsunamis?

"Earthquake prediction is something we haven't really been able to master yet," Sverdrup said. "With earthquakes, the best we can say is these are areas where earthquakes are likely to occur and this is our best estimate of the statistical probability of an earthquake of a certain size happening within a certain period of time."

Once an earthquake like this one has occurred, it's possible to assess whether or not it will generate a tsunami by determining whether a vertical shift occurred at the fault and by looking at measurements of water height recorded around the Pacific Ocean basin by the Tsunami Warning Network.

The warning network alerts people living in the area that will possibly be hit by a tsunami."Unfortunately, the closer you get to the earthquake, the less time you have. Clearly in the case of the country of Japan, they would not have had much warning at all," Sverdrup said.

With the westbound wave traveling at about 500 mph (804.7 kilometres per hour), roughly the speed of a commercial flight, Hawaii and the west coast of North America were better off.

In Japan, the tsunami warning went out about five minutes after the earthquake and included an estimated height for the waves, Yeh said. Reports of the time between the warning and the arrival of the giant waves varied, and as of Friday (March 11) afternoon, the death toll was still uncertain, with hundreds reported missing.

Yeh said the island nation was as well-prepared as it could have been for the disaster.

"It's a real problem in Japan, so they are always worried about tsunamis, they have tsunami drills and they have tsunami warnings," he said.

FULL STORY : LIVE SCIENCE