Floating islands almost 70 miles long of bodies and debris after the Japanese tsunami are causing chaos in Pacific shipping lanes.
Cars, tractors, boats and entire houses have been seen floating towards America after the March 11 earthquake.
The largest "island" of debris is 69 miles long, according to the US Navy's 7th Fleet, which is monitoring the floating rubbish.
"It is very large and it's a maritime hazard," said Lieutenant Anthony Falvo, the deputy public affairs officer for the US Navy's 7th Fleet. "It can do anything from piercing the hull of a ship to leaving dents or getting wrapped up in propulsion systems."
Experts say it could take up to two years for the debris to reach Hawaii and another year to hit America's west coast.
The US Navy is working with Japanese building companies to start breaking up the islands.
As Japan struggles to recover from the tsunami, a 7.4 magnitude aftershock hit the same north-east region.
Four people were killed and a further 100 were injured after the tremor shook the Miyagi prefecture late on Thursday night.
The quake caused widespread blackouts, motorway closures and swaying buildings as far away as Tokyo.
A tsunami warning was later lifted.
Damage was reported at the Onagawa nuclear power plant but radiation levels remained steady. The strong tremor also briefly halted work at the stricken Fukushima Daiichi power plant but caused no further damage.
The aftershock has done nothing to help the fraying nerves of survivors. Yesterday shoppers emptied shelves, traffic moved at a snail's pace after traffic lights lost power and drivers waited in long lines to buy petrol in a new wave of anxiety.
"I feel helpless. I am back to square one," said Ryoichi Kubo (52), who had just re-opened his gas station in hard-hit Iwate prefecture after the power outage and prolonged fuel shortage that followed the tsunami. Yesterday, he was again without electricity.
About 450,000 households were still without electricity last night, said Souta Nozu, a spokesman for Tohoku Electric Power Co. That includes homes in Japan's northwest that had been spared in the first quake. With power lines damaged, it was not clear whether normal operations would resume.
Several nuclear power plants briefly switched to diesel generators when the aftershock hit but were reconnected to the grid by yesterday afternoon. (© Daily Telegraph, London)