Pressure rising in second Japanese reactor

According to plant officials, reactor 3 has lost its emergency cooling system, a factor that led to a major explosion at reactor 1 at the plant on Saturday.

While the Japanese government is attempting to play down fears of a radiation leak at the Fukushima plant, the plant's operators, Tokyo Electric Power (Tepco), have said radiation levels around the plant had now risen above permissible limits.

Government spokesman Yukio Edano however acknowledged it was possible that a meltdown had occurred at reactor 3.

The BBC is also reporting that a meltdown at reactor 3 would be potentially more serious than at the other reactors, because it is fuelled by plutonium and uranium, unlike the other units which carry only uranium.

According to experts, as long as authorities can keep fuel rods in the core covered with water, they should be able to avoid a major disaster. Emergency workers were reportedly pumping in seawater to cool the rods, but one report suggested the tops of the rods had briefly been exposed.

Technicians opened valves at reactor 3, allowing small amounts of radioactive vapour to escape in a bid to reduce the pressure in the unit. A similar procedure was performed on the first reactor, hours before the explosion that wrecked the building it was housed in.

The Japanese government doubled the size of the evacuation zone around Fukushima 1 to 20km (12.4 miles) after the blast.

So far, about 170,000 people have been evacuated from the area near the plant. Meanwhile, police have warned that the death toll in tsunami-hit Miyagi prefecture alone could exceed 10,000.

Officials previously said that more than 2,000 people died or were missing following Friday's earthquake and tsunami. Millions remain without electricity and authorities are stepping up relief efforts as the scale of the tragedy becomes clearer.