A water recycling system crucial to progress at Japan's damaged nuclear power plant was halted for repairs on Monday after briefly resuming full operation.

Tons of fresh water has been pumped to cool the reactors since the Fukushima Daiichi plant was damaged by the March 11 earthquake and tsunami. That process taints the water with radiation, and 110,000 tons of contaminated water has accumulated and could overflow by early July.

Workers have struggled for weeks to use a new system that would clean the tainted water and reuse it in the cooling process. It fully operated for five hours earlier this month, and test-runs were conducted before it went fully operational and pumped treated water into the reactors on Monday.

But plant operator Tokyo Electric Power Co (TEPCO) said the system was halted about an hour and a half later. Workers spotted water leaking from a hose that was sending the processed water into the reactors, TEPCO spokesman Junichi Matsumoto said.

The system has reprocessed 1,850 tons of contaminated water.

The earthquake and tsunami destroyed power and cooling systems at the Fukushima plant, melting reactor cores and leaking massive amount of radiation. Some contaminated water had seeped into the ocean, causing criticism and concerns in and outside of Japan.

TEPCO and the government have said they hope to achieve a cold shutdown of the reactors by January by bringing the core temperatures to below 100 C.

TEPCO needs to decontaminate more than 100,000 tons of highly radioactive water that has built up during reactor cooling operations and prevented workers from accessing areas of the plant to make repairs.

The 9.0-magnitude earthquake triggered a tsunami that smashed into the Fukushima plant and knocked out reactor cooling systems, triggering meltdowns, explosions and radiation leaks in the world's worst nuclear accident since Chernobyl in 1986.

Japanese Prime Minister Naoto Kan's nuclear aide Goshi Hosono said it had "taken some time" to stabilize the processing of waste water. "That has led to delays in using the recycling system for cooling", he said.

"Factoring in delays and troubles, we wanted to start this circulation cooling by the end of this month. So I am relieved to have been able to come to this."

Japan's embattled prime minister has created two Cabinet posts to oversee the nuclear crisis and tsunami reconstruction efforts as he hopes to shore up his administration.

Kan on Monday named Ryu Matsumoto as reconstruction minister and made Hosono his minister in charge of handling the crisis. He also gave special advisory positions to two other senior politicians.

Kan is under pressure to resign because of a perceived lack of leadership following the disaster. He has said he would be willing to step down, but only after significant steps are made toward putting Japan's recovery on a solid footing.