Three hundred engineers have been struggling inside the danger zone to salvage the six-reactor Fukushima plant in the world's worst nuclear crisis since Chernobyl 25 years ago.

"I think the situation is improving step by step," Deputy Chief Cabinet Secretary Tetsuro Fukuyama told a news conference.

In one remarkable story of survival, an 80-year-old woman and 16-year-old youth were found alive under the rubble in the devastated city of Ishinomaki, nine days after the killer earthquake and tsunami, NHK public TV said, quoting police.

At the nuclear plant, workers braving high radiation levels in suits sealed in duct tape managed to connect power to the No. 2 reactor, crucial to their attempts to cool it down and limit the leak of deadly radiation.

Officials at plant operator Tokyo Electric Power Company (TEPCO) said the workers aimed to restore the control room function, lights and the cooling at the No. 1 reactor, which is connected to the No.2 reactor by cable.

But rising cases of contaminated vegetables, dust and water have raised new fears. The government has prohibited the sale of raw milk from Fukushima prefecture and spinach from another nearby area. It is considering further restrictions on food.

Tokyo, just 240 km (150 miles) south of the crippled plant and where the government said it had found traces of radioactive iodine, was subdued on Sunday but there was no sense of panic.

"There's no way I can check if those radioactive particles are in my tap water or the food I eat, so there isn't much I can really do about it," said Setsuko Kuroi, an 87-year-old woman shopping in a supermarket in the capital with a white gauze mask over her face.

"I don't plan big changes to my diet. And I only drink bottled water."