By Mari Saito

TOKYO (Reuters) - Japan may use emergency reserve funds from this year's budget to help Tokyo Electric Power Co, the operator of the crippled Fukushima nuclear plant, deal with escalating radioactive water problems at the site.

Tokyo Electric, or Tepco, acknowledged last week that hundreds of tonnes of highly radioactive water had leaked from a tank, one of around 350 assembled quickly after the 2011 earthquake and tsunami that triggered nuclear meltdowns at the site. The tanks are used to store water pumped through the reactors to keep fuel in the melted cores from overheating.

The latest revelation is the most serious problem in a series of recent mishaps, including power outages, contaminated workers and other leaks. Tepco also said last month - after repeated denials - that the Fukushima plant was leaking contaminated water into the Pacific Ocean from trenches between the reactor buildings and the shoreline.

"It's deplorable," Chief Cabinet Secretary Yoshihide Suga told a news conference on Monday. "It is necessary for the country to step forward and offer support to solve the problem as well as prevent a recurrence."

Suga said trade and industry minister Toshimitsu Motegi had been instructed to come up with measures, including the possible use of reserve funds from the state budget for the year ending March 2014. Japan put aside a total of 350 billion yen (2.28 billion pounds) in reserves for natural disasters and other emergencies in the budget.

Motegi and Tepco President Naomi Hirose will visit the Fukushima site later on Monday.

Japan is under increasing pressure to contain the toxic water problem at the plant. The new crisis comes as Prime Minister Shinzo Abe is pitching the country's nuclear technology abroad to countries like Turkey, promising that its nuclear reactor makers have learned vital safety lessons from the disaster.

Tepco shares fell as much as 10 percent on Monday to their lowest in 12 weeks.

CHERNOBYL LESSONS

Foreign Minister Fumio Kishida on Sunday visited Chernobyl in Ukraine, the site of the 1986 nuclear disaster, and said he hoped to apply lessons learned there to Fukushima.

"I directly saw that the battle to contain the accident still continues 27 years after the disaster. Ukraine's experience and knowledge serve as a useful reference for workers coping with the Fukushima nuclear crisis," the Kyodo news agency quoted Kishida as telling reporters.

China on Sunday said it was paying close attention to developments at Fukushima, noting it has the right to request entry into waters near the facility to conduct checks and assess the impact of the nuclear accident on the Western Pacific.

The country's State Oceanic Administration said it hadn't found any evidence of a "direct impact" from radiation on Chinese waters, but will closely monitor developments.

Public distrust towards Tepco's handling of the Fukushima plant clean-up has also intensified, with a Mainichi newspaper poll finding 91 percent of respondents saying the government should take a more active role in the contaminated water issue.

(Additional reporting by David Stanway in Beijing, and Leng Cheng and Tetsushi Kajimoto in Tokyo; Editing by Linda Sieg and Ian Geoghegan)