Japanese emergency crews have battled to stabilise the crippled Fukushima Daiichi (No. 1) atomic power plant that has sparked global fears of a large-scale radiation disaster.

The 1970s era plant was rocked by the 9.0-magnitude quake on March 11 and then hit by the 14-metre (46 foot) tsunami it triggered, cutting it off from the national electric grid and knocking out backup power systems.

This shut down the cooling systems needed to keep the fuel rods inside reactors, and spent rods in containment pools, from overheating and boiling off the water around them, then melting down and releasing large-scale radiation.

To stop a catastrophe, crews have doused the reactors and pools with thousands of tons of seawater from fire engines and concrete pouring trucks.

Hydrogen explosions have blown away or damaged outer containment buildings around the steel-and-concrete primary reactor containment vessels.

As the dousing continues, sending radioactive vapour into the sky, workers have laid new power lines to all six reactors and are working to relaunch the original cooling systems. Here is the latest known status of the six reactors:

REACTOR ONE -- Overheating caused a partial meltdown of the reactor core. A hydrogen blast blew away the roof and walls of the outer building.
The control centre has partial power and lighting again.

REACTOR TWO -- Also thought to have suffered a partial meltdown. Fuel rods in pool were fully exposed at one stage. The outer structure was damaged by the explosion of adjacent number three.

REACTOR THREE -- A hydrogen explosion badly damaged the outer building, and a partial meltdown is also suspected. The reactor is the only one to use a volatile uranium-plutonium mix. Black smoke billowed from the site this week. The control room has partial power and light again since Tuesday, and workers were trying to reconnect a water pump to the suppression pool.

REACTOR FOUR -- The plant was undergoing maintenance when the quake struck and there are no rods in the reactor core. However the spent fuel storage pool has been heating up, threatening to run dry. A fire has destroyed the roof of the outer containment structure.

REACTOR FIVE -- Under maintenance when quake hit. External, non-emergency power connection has been restored and cooling of the spent fuel pool has resumed. One water pump failed Thursday and was going to be replaced.

REACTOR SIX -- Also under maintenance when the tremor hit, emergency power generator and cooling functions have been restored.

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