Survivors of Japan's worst recorded earthquake and a tsunami huddled in shelters and hoarded supplies on Saturday as rescue workers searched the rubble of a coastline choked by cars, boats and levelled homes.

Aerial footage showed buildings and trains strewn like children's toys after a deluge of seawater swept into fields around the city of Sendai, about 130 km (80 miles) from the epicenter of the earthquake and among the worst-hit areas.

Radiation leaked from an unstable nuclear reactor in Fukushima prefecture, near Sendai, a port of 1 million people known in Japan as the "City of Trees" and cradled by dormant volcanoes.

In districts around Fukushima, a city about 67 km (42 miles) south of Sendai, many survivors lined up for drinking water in town centres, filling teapots and plastic containers, while Japan's Self-Defense Force officers searched for missing people. 

In Iwanuma, not far from Sendai, people spelled S.O.S. on the roof of a partially submerged hospital, one of many desperate scenes in the area.

Hundreds of fishing vessels, many upturned, stood stranded in the fields, washed inland by the walls of water. In shelters across the region, residents wrapped themselves in blankets, some clutching each, while others sobbed.

At least 1,300 people were killed by the earthquake, the world's fifth most powerful in the past century.

Tens of thousands were forced to evacuate across Japan's northern region, their homes crushed by the 10-metre (33-foot) tsunami.

Off Japan's northeastern coast, an oil tanker lay eerily stranded in shallow water. Inland, in Sendai, a black mini-van perched perilously on a metal post.

Power and cellphones remained down for much of the region.

In Mito, another town in the area, long lines formed outside a damaged supermarket as hundreds waited for medicine, water and other supplies. Supplies ran low as people stocked up, not knowing how long it would take for fresh goods to arrive.

"All the shops are closed, this is one of the few still open. So I came to buy and stock up on diapers, drinking water and food," Kunio Iwatsuki, 68, told Reuters.

In the nearby town of Oarai, survivors crammed into a school gymnasium turned into a shelter.

In Tokyo, where many have long feared the prospect of another monster earthquake of the scale that killed about 140,000 people in 1923, residents struggled to come to terms with damage inflicted on the country and their city.

Some were relieved the damage in the capital was not greater, but many remained panic-stricken about the continuing chaos elsewhere, especially as radiation leaked from the nuclear reactor in Fukushima prefecture.

"People make manuals for earthquakes, but when the earthquake actually happens, can you actually follow the manual?" said 60-year-old officer worker Kiyoshi Kanazawa.

"Everyone runs away when things are shaking, and they ask you to stop the gas and fire in your house, but you do not have enough space for this in your brain." – Reuters