Construction starts on shelters in Rikuzentakata, Iwate prefecture, to house the thousands of residents made homeless by Japan's earthquake and tsunami Reuters

The human and financial cost of the tsunami continues to rise, after police estimates showed more than 18,000 people have died in the disaster and the World Bank said it may cost Japan as much as £145bn to repair the damage.

The figures came as emergency workers were evacuated from the Fukushima Daiichi nuclear power plant after smoke or steam was seen rising from one of its reactor units.

The smoke raised concerns that water in the spent fuel pools at the No 3 unit was running low, but officials said there was no immediate spike in radiation levels.

"We are checking the cause of the smoke," Hidehiko Nishiyama, a nuclear safety agency official, told reporters.

Earlier, engineers finally succeeded in connecting power cables to three of the plant's reactors and said they planned to test the pumps soon.

Engineers hope to connect those power supplies to the No 3 and No 4 units on Tuesday, the public broadcaster NHK said.

The nuclear emergency is far from over, however. On Monday, it was reported that the No 3 reactor had experienced a surge in pressure that may require workers to vent radioactive steam, a tactic that set off hydrogen gas explosions at the facility last week.

The government's chief spokesman, Yukio Edano, conceded that the buildup of pressure was unsettling. "We knew that even if things went smoothly, there would be twists and turns," he told reporters. "At the moment, we are not so optimistic that there will be a breakthrough."

That is causing concern because the reactor is the only one of the six that contains plutonium-uranium mixed oxide fuel – or MOX – and would release highly toxic plutonium in the event of a meltdown. The fuel in the other reactors is uranium.

The country's self-defence forces resumed work on Monday to cool down the No 4 and No 3 reactors with seawater. Japan's nuclear safety agency said it did not believe much water from the two reactors had seeped underground.

Radiation leaks from stricken reactors continued to spread through the region's food supply, though at levels too low to endanger health.

The agency acknowledged that workers at the site risked inhaling radioactive dust, but said it had so far found no evidence of that happening.

Radiation in excess of government standards was found in canola and chrysanthemum greens grown in the Fukushima area, a day after authorities reported that milk and spinach had been contaminated, as well as tap water in Tokyo, 150 miles away.

The health ministry advised 6,000 villagers in Iitate, 19 miles from the power plant, not to drink tap water after tests revealed it contained abnormal, though not harmful, amounts of iodine-131, a radioactive substance.

"We think we have arrived at the point where we are very close to getting the situation under control," the deputy cabinet secretary, Tetsuro Fukuyama, said.

Graham Andrew, a senior official of the International Atomic Energy Agency, said: "There have been some positive developments in the last 24 hours but overall the situation remains very serious."

The US energy secretary, Steven Chu, told CNN that he believed the worst of the nuclear crisis was over, but added: "I don't want to make a blanket statement."

Attention is turning to the humanitarian crisis on Japan's north-east coast and the cost of the cleanup and reconstruction operations.

The World Bank said that it could take Japan five years, and cost between £75bn and £145bn – equivalent to 4% of Japan's GDP – to overcome the catastrophe, while private insurers face a combined bill of up to $33bn.

"Damage to housing and infrastructure has been unprecedented," the bank said. "Growth should pick up though in subsequent quarters as reconstruction efforts, which could last five years, accelerate." The bank said damage from the tsunami could also affect trade in the region.

The price of some Japanese-made memory chips have risen 20% because of disruption to production lines, while car plants in Asia face shortages of auto parts. "Disruption to production networks, especially in automotive and electronics industries, could continue to pose problems," the World Bank said. "Japan is a major producer of parts, components and capital goods which supply east Asia's production chains."

While hundreds of workers battle to render the nuclear plant safe, Japan continues to count its dead. Police estimates show more than about 18,400 died – 10,500 in Miyagi prefecture alone. A further 452,000 people are living in shelters. "It is very distressing as we recover more bodies day after day," said police spokesman Hitoshi Sugawara.