- Rescuers found them after responding to their shouts
The report was greeted with scepticism at first following claims on Saturday that a young man had been found alive in his house after clinging to life for eight days - when in fact he had returned to his home from a shelter.
But police in the Mikako prefecture were insisting that there was no mistake about the two people found alive under rubble today.
No immediate details were available apart from police saying that rescuers were scouring debris when they found the elderly woman and the young man.
'They were in a very weakened state, but have responded to initial treatment by the rescuers,' said a police spokesman.
Police said the two were found in the city of Ishinomaki, nine days after the earthquake and tsunami, a survival which has stunned medical teams.
It was revealed the pair are a grandmother and her grandson.
The Japanese TV network NHK quoted police in Miyagii prefecukrre as saying the elderly woman and the teenager had responded to shouts from a police rescue team
At Ishinomomaki's Red Cross hospital, where the survivors had been taken, a spokesman said they were receiving treatment.
'I had only a glimpse of the elderly woman, who had her eyes closed,' said the spokesman. 'She didn't appear to be dead.'
The remarkable news comes as authorities today announced they had restored power to the Fukushima plant.
Three hundred engineers have been struggling inside the danger zone to salvage the six-reactor 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.
The 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, Kyodo news agency said.
It added that plant operator Tokyo Electric Power Company (TEPCO) 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 and the government said it will decide by Monday on whether to restrict consumption and shipments of food from the quake zone.
Police said they believed more than 15,000 people had been killed by the double disaster in Miyagi prefecture, one of four in Japan's northeast that took the brunt of the tsunami damage. In total, more than 20,000 are dead or missing, police said.
The unprecedented crisis will cost the world's third largest economy as much as $248 billion and require Japan's biggest reconstruction push since post-World War Two.