Radiation readings around tanks holding contaminated water at the crippled Fukushima Daiichi nuclear plant have spiked by more than a fifth to their highest levels, Japan's nuclear regulator said Wednesday, heightening concerns about the cleanup of the worst atomic disaster in almost three decades.

Radiation hot spots have spread to three holding areas for hundreds of hastily built tanks storing water contaminated by being flushed over three reactors that melted down at the Fukushima Daiichi plant in March 2011.

The rising radiation levels and leaks at the plant further inflamed international alarm, one day after the Japanese government said that it would step in with almost $500 million of funding to fix the growing levels of contaminated water at the plant.

Readings just above the ground near a set of tanks at the plant showed radiation as high as 2,200 millisieverts (mSv), Japan's Nuclear Regulation Authority (NRA) said Wednesday. The previous high in areas holding the tanks was the 1,800 mSv recorded Saturday.

Both levels would be enough to kill an unprotected person within hours. The NRA has said the recently discovered hot spots are highly concentrated and easily shielded.

The revelations came just days before the International Olympic Committee decides whether Tokyo -- 140 miles from the wrecked plant -- will host the 2020 Olympic Games, and the government is keen to show that the crisis is under control. Madrid and Istanbul are the rival candidates.

"The world is watching to see if we can carry out the decommissioning of the Fukushima nuclear power plant, including addressing the contaminated water issues," Prime Minister Shinzo Abe told Cabinet ministers, who met to approve the plan.

The government intervention responds to only a tiny slice of the Fukushima crisis triggered by the 2011 earthquake and tsunami, which destroyed safety sytems and caused three reactor meltdowns. The cleanup, including decommissioning the ruined reactors, will take many decades and likely rely on unproven technology.

The measures do not address the full problem of water management at the plant or the bigger issue of decommissioning. The sensitive job of removing spent fuel rods is to start in the coming months. The ultimate fate of the plant's operator, Tokyo Electric Power Co. (TEPCO), also remains unclear, as does the question of who will eventually foot the bill: Japanese taxpayers or the embattled TEPCO.

"This is a matter of public safety, so the country has to take the lead on this issue and respond as quickly as possible," Economics Minister Akira Amari told a news conference. "Figuring out who to bill for the costs can come later."

Chief Cabinet Secretary Yoshihide Suga told a separate news conference that the government would spend a total of $473 million, including $210 million in emergency reserve funds from this year's budget.

Of that, $320 million will fund the building of a massive underground wall of frozen earth around the damaged reactors to contain groundwater flows, and $150 million will be spent to improve a water-treatment system meant to drastically reduce radiation levels in the contaminated water.