Japan’s nuclear crisis has the country, and the world, on edge.

How is the country coping, who is at risk from radiation leaks, and could it become another Chernobyl? Sky gives the breakdown.

Who is at risk from the radiation leaks?

At the moment the highest risks appear to be limited to an area immediately around the plant.

People living within 18 miles (30km) of the facility have now been urged to stay indoors.

Radiation levels in the city of Maebashi, 85 miles (140km) south of the plant were reported to be up to 10 times normal levels but there has been disagreement among foreign experts whether this is harmful.

The UN weather agency says that winds are now dispersing radioactive material over the Pacific Ocean and away from Japan and other Asian countries.

Japan’s Prime Minister Naoto Kan has however warned the nation that the “possibility of further radioactive leakage is heightening”.

What will happen?

Assessments vary because of the limited amount of data that is being made available to external experts.

Japanese media are increasingly critical of the Government and Tokyo Electric Power (TEPCO), the company that runs the plant, for failing to provide enough information on the incident.

Japan’s Prime Minister is himself reported to have asked TEPCO “what the hell is going on”.

The key issue is what happens to the radioactive reactor fuel and whether the fuel rods are breaking up or in the worst case whether the fuel is melting.

Four of the six reactors at Fukushima 1 have overheated.

Three of these four have suffered explosions and there has been a fire at the fourth.

Despite these incidents and the earlier quake and tsunami experts say the indications are that the critical inner steel containment shields around the reactor fuel rods are all intact.

What caused the crisis?

Although not fully established it appears the earthquake resulted in the plant losing electric power from the main grid as well as its back up system of diesel generators and batteries.

Without electricity the water cooling system failed, leading to overheating and a rise in pressure.

Could it become as serious as the Chernobyl nuclear accident?

There is general agreement that it will not get as bad as the 1986 nuclear disaster in Ukraine which was rated at a maximum seven on the international scale of gravity for nuclear accidents.

Japan has rated the Fukushima incident at four on the scale but France’s nuclear watchdog has rated it at level six.

Yukiya Amato, the head of the International Atomic Energy Agency, the IAEA has said “the development of this accident into one like Chernobyl is very unlikely”.

The Chernobyl reactors were very different to those at Fukushima and the safety features at the Ukraine facility were antiquated compared to those in place in Japan.

Despite that, experts say that it is too early to say whether a catastrophe has been averted.