Smoke and steam rose from two of the most threatening reactors at Japan's quake-crippled nuclear plant today, suggesting the battle to avert a disastrous meltdown and stop the spread of radiation was far from won.
The world's worst nuclear crisis in 25 years playing out 240km north of Tokyo was triggered by a huge earthquake and tsunami on March 11 that has left at least 21,000 people dead or missing.
Technicians working inside an evacuation zone around the stricken Fukushima Daiichi plant on Japan's north-east Pacific coast have attached power cables to all six reactors and started a pump at one of them to cool overheating nuclear fuel rods.
But steam appeared to be rising from reactor No 2 and white haze was detected above reactor No 3. There have been several blasts of steam from the reactors during the crisis, which experts say probably released a small amount of radioactive particles.
Plant operator Tokyo Electric Power Co (TEPCO) said later the smoke had turned to steam and it was deemed safe to continue work in bringing the plant under control.
Away from the plant, mounting evidence of radiation in vegetables, water and milk stirred concerns among Japanese and abroad despite officials' assurances that the levels were not dangerous.
TEPCO said radiation was found in the Pacific Ocean nearby, not surprising given rain and the hosing of reactors with seawater. Some experts said it was unclear where the used seawater was ultimately being disposed.
Radioactive iodine in the sea samples was 126.7 times the allowed limit, while caesium was 24.8 times over. That still posed no immediate danger, TEPCO said.
"It would have to be drunk for a whole year in order to accumulate to one millisievert," a TEPCO official said, referring to the standard radiation measurement unit. People are generally exposed to about 1 to 10 millisieverts each year from background radiation caused by substances in the air and soil.
Japan has urged some residents near the plant to stop drinking tap water after high levels of radioactive iodine were detected. It has also stopped shipments of milk, spinach and another vegetable called kakina from the area.
Experts say readings are much lower than around Chernobyl after the 1986 accident.
The World Health Organisation (WHO) said the radiation impact was more serious than first thought, when it was expected to be limited to 20-30 km from the plant.
Experts have offered a glimmer of hope in Japan's darkest time since World War Two, saying the situation appeared to be improving at the Fukushima plant, especially after more advances than setbacks in the past 48 hours.
The priority today will be patching up the No 2 reactor so electricity, already connected, can be turned on.
By this morning, reactor No 1 was receiving power and No 5 had both electricity and working cooling pumps.
The prospects of a nuclear meltdown in the world's third-biggest economy -- and its key position in global supply chains, especially for the automobile and technology sectors -- rattled investors worldwide last week and prompted rare joint currency intervention by the G7 group of rich nations.
Tokyo stocks were up at more than 3pc in the early afternoon after a holiday yesterday, following a rise in global stocks as progress in the nuclear crisis revived risk appetite. The yen slid on speculation of more G7 intervention.
Damage from the earthquake and tsunami is estimated at e176bn, making it the world's costliest natural disaster.