Japanese emergency crews have battled to stabilise the crippled Fukushima 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, which can lead to 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.

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. Workers have injected pure water into the pressure vessel via a pump, but the cooling system has not been restored yet.

The basement of the adjacent turbine building was flooded with radioactive water, and workers had begun pumping the liquid out.

On Monday, radioactive water was discovered in a trench outside the turbine building, 56 meters from the ocean. Tepco officials did not rule out contaminated water may have seeped into ocean.

REACTOR TWO — Also thought to have suffered a partial meltdown. Fuel rods in pool were fully exposed at one stage.

A puddle of highly contaminated water was found in the basement of the turbine building and outside in a trench, where over 1,000 milli-sieverts per hour was measured.

Workers injected pure water with added boric acid into the pressure vessel via a temporary electric pump after switching from a fire pump.

Tepco announced on Monday that the reactor’s spent fuel pool is now submerged in water and in a stable condition.

REACTOR THREE — A hydrogen explosion badly damaged the outer building, and a partial meltdown is also suspected.

Three workers were exposed to high levels of radiation on Thursday when they stepped through contaminated water at the basement of the turbine building. They left hospital on Monday with no visible injuries.

Workers began injecting pure water into the pressure vessel on Monday.

Water was also found in the trench outside the turbine building, but rubble prevented the workers from accessing the site.

REACTOR FOUR — The plant was undergoing maintenance when the quake struck and there are no rods in the reactor core. Contaminated water was found in the basement of the turbine building but workers have yet to remove it.

Fire-fighters have doused the spent fuel pool using a concrete pumping vehicle. Tepco announced on Monday its spent fuel pool is now submerged in water.

REACTOR FIVE — Under maintenance when quake hit. External, non-emergency power connection has been restored and cooling of the spent fuel pool has resumed. A damaged heat-removal pump has been replaced.

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