Thailand's opposition lashed out Wednesday at Prime Minister Yingluck Shinawatra's financial plans for dealing with the worst floods in half a century, saying the economy was under threat.

Her main rival Abhisit Vejjajiva, leader of the Democrat Party, urged Yingluck to forgo certain populist spending policies such as help for first-time home and car buyers and to divert the money to flood victims.

"The government has not reviewed and prioritised the economy and therefore is jeopardising the next phase of economic management," said the former premier, who was replaced by Yingluck after a July election defeat.

He was speaking during a parliamentary debate on the 2012 national budget, which earmarks total spending of about 2.4 trillion baht ($78 billion) -- some 400 billion baht less than expected revenue.

Yingluck's plan to raise 120 billion baht for flood relief by asking each ministry to allocate 10 percent of its budget was "unrealistic," added Abhisit.

The Thai floods, triggered by months of unusually heavy rains, have killed 529 people and damaged the homes and livelihoods of millions around the country.

The waters also forced the closure of thousands of factories -- interrupting global supply chains, putting more than half a million people temporarily out of work and costing the economy billions of dollars.

Abhisit noted that the government's forecast of 3.5-4.0 percent economic growth this year was higher than the central bank's projection of 2.6 percent.

Yingluck, a political novice and sister of fugitive former premier Thaksin Shinawatra who only came to power in August, has been under enormous pressure to tackle the three-month-old flood crisis.

Yingluck's administration has faced criticism for its confusing information about the floods and has angered some residents with its efforts to keep central Bangkok dry at the expense of outlying areas.

The former businesswoman is skipping an Asia-Pacific summit in Hawaii this weekend, postponing her debut on the world stage to deal with the floods, which are advancing deeper into the capital, home to 12 million people.

The finance ministry estimates the financial cost of the floods at 180 billion baht and expects 2011 economic growth will be cut by 1.7 percentage points because of the disaster, but still exceed 2.0 percent.