Japanese engineers have successfully attached a power cable to a tsunami-crippled nuclear station in a race to prevent deadly radiation. It is still unknown whether that will be enough to restart water pumps needed to cool overheated nuclear fuel rods.

The plant's operator Tokyo Electric Power Corporation said it has connected the external transmission line with the receiving point of the plant and confirmed that electricity can be supplied.

The next stage will be to check equipment is working and not damaged before trying to crank up the coolers at reactor Number 2, followed by 1, 3 and 4. If that works, it will be a turning point. That method was used to seal huge leakages from the 1986 Chernobyl disaster.

On Friday, Japan's Nuclear and Industrial Safety Agency upgraded the nuclear accident seriousness level at the Fukushima number-one nuclear power plant from four to five. The upgrade means the leak is on a par with the Three Mile Island accident in the United States in 1979.