Highly radioactive water has been found for the first time outside one of the reactor buildings at Japan's quake-hit Fukushima nuclear plant, officials say.
The leak in a tunnel linked to the No 2 reactor has raised fears of radioactive liquid seeping into the environment.
Plutonium has also been found in soil at the plant, but not at levels that threaten human health, officials say.
Earlier, Japan's government strongly criticised the plant's operator, Tepco, over mistaken radiation readings.
Tepco announced on Sunday that a highly radioactive pool of water in the No 2 reactor was 100 times more radioactive than it actually was.
Officials said the radiation scare was caused by a partial meltdown of fuel rods.
Underground tunnel
The discovery of highly radioactive water outside a reactor building is a worrying development, says the BBC's Mark Worthington in Tokyo.
Up until now, pools of water with extremely high levels of radiation have only been detected within the reactor buildings themselves.
The water was found in an underground maintenance tunnel, with one end located about 55m (180ft) from the shore.
Radiation levels were measured at 1,000 millisieverts an hour, a dose that can cause temporary radiation sickness. This is the same as the levels found on Sunday.
However, Tepco said there was no evidence that the contaminated water had reached the sea.
Tepco later said that plutonium had also been detected in soil at five locations at the plant but not at levels that represented a risk to human health.
It said the results came from samples taken a week ago and would not stop work at the plant.
Plutonium was used in the fuel mix for only one of the six reactors, number three.
The twin discoveries came hours after the government criticised Tepco for issuing incorrect readings from the plant.
On Sunday Tepco said radiation levels at reactor No 2 were 10 million times higher than normal before correcting that figure to 100,000.
"Considering the fact that the monitoring of radioactivity is a major condition to ensure safety, this kind of mistake is absolutely unacceptable," said Chief Cabinet Secretary Yukio Edano.
Tepco has apologised but the mistaken reading at the Fukushima Daiichi plant has called into question the operating company's handling of the current crisis, our correspondent says.
Tepco has been criticised for a lack of transparency and failing to provide information more promptly and for making a number of mistakes, including worker clothing.
Two workers were taken to hospital last week after wading though contaminated water with inadequate protection. They were expected to be released on Monday.
Foreign aid
Workers are battling to restore power and restart the cooling systems at the stricken nuclear plant, which was hit by a quake and tsunami over two weeks ago.
A 9.0-magnitude earthquake on 11 March and the powerful tsunami it triggered is now known to have killed 10,901 people, with more than 17,000 people still missing.
More than 190,000 people are living in temporary shelters.
The BBC's Roland Buerk in Rikuzentakata, Iwate prefecture, says prefabricated houses are being wired for electricity, but there is initially room for only 150 of the 1,000 survivors there.
In Miyagi prefecture - another of the worst-hit areas - the authorities estimate it will be three years before all of the rubble and debris has been cleared.
Some 20,000 US troops are bolstering Japan's Self-Defence Forces, delivering aid in what is said to be the biggest bilateral humanitarian mission the US has conducted in Japan.
As well as shortages of food, water and fuel, survivors are also having to endure frequent aftershocks.
Japan lifted a tsunami warning earlier on Monday that was issued after a 6.5-magnitude quake struck off the northern coast.
It is not reported to have caused any injuries or damage.
For the first time since the disaster, the government has permitted a foreign medical team to enter the country to treat victims, the Japan Times reports.
The health ministry has lifted a ban on holders of foreign medical licences from practising in Japan, allowing a team of 53 medical aid workers from Israel, including 14 doctors and seven nurses, to work.
