Rescue teams are only just reaching many coastal communities destroyed by the tsunami in Japan four days ago.
Many survivors are living in temporary evacuation centres such as schools.
Relief efforts are now being hampered by freezing weather, with Red Cross medical staff reporting cases of hypothermia.
Thousands of survivors of the huge magnitude 9 earthquake and 10 metre tsunami on Friday have spent a fourth night night without water and power, as authorities grapple with the scale of the disaster.
The death toll has risen to more than 2400 with at least 15,000 unaccounted for, broadcaster NHK said.
However, a survey by Japan's Kyodo news agency found local officials had lost contact with about 30,000 people, raising concerns of a dramatic increase in the toll.
Red Cross worker Patrick Fuller said the situation in the northeast of the country is "absolutely nightmarish".
"It's a scene from hell," he told Reuters from the coastal town of Otsuchi, in Iwate prefecture.
Mr Fuller says almost everything had been flattened. A 600-kilometre stretch of coastline was devastated by the tsunami.
He says water is still trapping many people in their homes, and aid teams are struggling to supply survivors with food and drinking water.
The principal of a school converted into a shelter at Rikuzentakata says people are physically and mentally exhausted; there is not enough food for three meals a day; there is no heating; and sanititation is a problem, with too few makeshift toilets for 1800 people.
The village of 24,500 people in the Iwate prefecture was nearly flattened.
Meanwhile, authorities have taken drastic steps to conserve power, ordering planned blackouts for the first time.
Highways and rail lines from northeast Japan are also disrupted, preventing deliveries of food and other goods to Tokyo.