The announcement came a day after China expressed concern at the discharge of contaminated water from the Fukushima Daiichi plant smashed by last month's earthquake, reflecting growing international unease over the month-long nuclear crisis.
"We are working on releasing water ... we are likely to finish this tomorrow," Hidehiko Nishiyama, a deputy director- general at Japan's Nuclear and Industrial Safety Agency, told reporters on Saturday.
Plant operator Tokyo Electric Power Co (TEPCO) said earlier it expected to stop pumping tainted water into the sea on Saturday, but work was interrupted by a powerful aftershock on Thursday.
TEPCO is struggling to contain the worst atomic crisis since Chernobyl. Engineers say they are far from in control of the damaged reactors and it could take months to stabilize them and years to clear up the toxic mess left behind.
Nuclear reactor maker Toshiba Corp has proposed a 10-year plan to decommission four of the six damaged reactors at the plant, 240 km (150 miles) north of Tokyo, said Kyodo news agency.
But the government has said it was too early to have a "specific road map" for ending the crisis.
The magnitude 9 earthquake and tsunami on March 11 left 28,000 people dead or missing, and northeastern Japan a splintered wreck.
More than 153,000 people affected by the tsunami and radiation are living in school gymnasiums and other evacuation centers, according to the National Police Agency. Several tsunami-damaged cities have begun moving families into temporary housing, NHK state television said.
Banri Kaieda, a minister whose portfolio includes the nuclear industry, said he hoped evacuees from the radiation zone in Fukushima could visit their homes as soon as possible.
Japan has made evacuation mandatory for people living within a 20 km (12-mile) radius of the crippled reactor and urged those living between 20 km and 30 km from the plant to stay indoors.
"There were expectations among the evacuees that they could return to their homes for one night, but they will only be able to stay for a few hours to gather their personal belongings," Kaieda was quoted by Jiji news agency as saying in Fukushima.
GLOBAL RADIATION CONCERNS
Several countries have restricted food imports from Japan over radiation fears as Japan's economy reels from the country's worst disaster since World War Two.
Food is a tiny part of Japan's export-oriented economy, but disruptions to its manufacturing and electronics supply chains are reverberating around the world.