The demonstrators, followers of ousted Prime Minister Thaksin Shinawatra, say Abhisit's government came to power through illegal means and are demanding a dissolution of Parliament and fresh elections.

"Is he (Abhisit) trying to buy us off?" said a protest leader, Nattawut Sai-kua. "It is not going to work. We will protest until this illegitimate government is gone."

The "red-shirts," as they are commonly known because of their favored color, say Abhisit rose to power through illegal means — after courts, backed by the powerful military, removed two previous pro-Thaksin administrations last year.

The court action ended one of Thailand's worst political crises: Months of protests by Thaksin's opponents who brought the government to a virtual standstill and severely damaged the country's vital tourist industry by occupying both the prime minister's office compound and the capital's two airports.

Protesters on Thursday said they planned to demonstrate at Government House for at least three days but have promised not to enter the compound. Their earlier protests have been generally peaceful.

As dusk approached, the number of protesters swelled to more than 20,000, Metropolitan Police Commander Lt. Gen. Worapong Chiwpreecha said. About 10,000 police and soldiers were deployed for the demonstration, he said.

Abhisit said the government does not expect the protest to turn violent.

"We will use utmost patience," he told reporters. "The government wants the situation to be peaceful so the country can move forward."

The so-called "help-the-nation" dole-out scheme targets over 9 million people earning less than 15,000 baht ($424) a month.

"What we intend to do is get the economy through this very difficult period," Abhisit said after handing out the first check to a teacher at the launch of the 18 billion baht ($509 million) program. "We need to get money quickly into the system, and this is the quickest way."

Thailand has been hit with its worst economic downturn since the 1997 Asian financial crisis. Southeast Asia's second largest economy grew 2.6 percent in 2008. But it is expected to contract 2.5 percent this year, as the country's crucial export sector has slid for four months straight.

Stores and shopping complexes were quick to jump in, hoping to attract check recipients with special deals.

"The check is valued 20 percent higher if you cash it in at our store," said Chamnan Metapreechakul, senior marketing director for the Mall Group, one of Thailand's largest mall operators. "We expect people to spend it because it's not large enough to save."

At the Kentucky Fried Chicken fast food chain, a check can be exchanged for store coupons with 20 pieces of chicken thrown in for free.

"It feels good that I am spending to save the country. What an odd concept!" said Narisara Songsawang, a 36-year-old clerk.

But some demonstrators donated the windfall they received from the government to the protest movement, protest leaders said.

The program is expected to increase economic growth by 0.2 percentage points, Finance Minister Korn Chatikavenij said Wednesday.

The first lot of 5.5 million checks issued Thursday will be followed by 1.2 million in late March and the rest in early April.

Some said they planned to save the money for hard times.

"You watch the news and people are getting laid off daily. I think I will save it in case my husband is the next one to lose his job," said Ponnapa Sintanee, a 38-year-old mother of three. She earns 12,000 baht ($340) a month as a school teacher.

Although the one-time measure was welcomed by many, some criticized it for targeting only about a third of the country's labor force who are registered with the Social Security Fund. Those in the informal sector, including farmers and self-employed people, are not eligible.

Abhisit said the government plans to launch other programs for those left out of the current scheme.