United States President Barack Obama has signed his hard-fought economic stimulus plan after Congress approved the $US787 billion package last week.
At a signing ceremony in Denver, Mr Obama said it was "the most sweeping recovery package in our history".
The signing of the massive stimulus measure is designed to start the flow of federal money towards infrastructure projects, healthcare, renewable energy development and conservation programmes.
The approved version of the plan is split into 36% for tax cuts and 64% in spending and money for social programmes.
The White House has said it will take about a month for the money to start flowing from the package. Some economists, however, believe the measures will come too late to have any effect in 2009 when many forecasters predict full-year output will contract.
The package includes working-class tax cuts, infrastructure spending, help for the poor and unemployed and investment in alternative energy.
Mr Obama has predicted that the stimulus plan will save or create more than 3.5 million jobs over the next two years. "I don't want to pretend that today marks the end of our economic problems, nor does it constitute all of what we're going to have to do to turn our economy around, but today does mark the beginning of the end."
He said part of the plan would put Americans back to work in critical areas such as roads and rail infrastructure. "[Today is] the beginning of first steps to set our economy on a firmer foundation."
The plan got no Republican support in the House of Representatives and just three Republican votes in the Senate.
Republicans say the tax cuts are insufficient, and that the economy will be saddled with debt for years to come.
US stocks slid on Wednesday, sending Wall Street near bear-market lows and tracking other global markets, which sank on fears that government action will not be enough to pull the US out of recession and avert a deepening worldwide financial crisis.
The bill also includes a contentious "Buy American" provision that, despite being watered down, has angered US trading partners.
On Monday, Brazilian Foreign Minister Celso Amorim threatened to challenge the legality of the clause at the World Trade Organisation.
"It's a complex legal analysis, but we're doing it," Mr Amorim said. "Going to the WTO is a real option."
The approved plan stipulates that public works and building projects funded by the stimulus use only US-made goods, including iron and steel.
The EU and Canada had earlier said that provisions favouring American-produced materials for government projects risked provoking retaliatory protectionist measures.
Earlier this month, Brazilian President Luiz Inacio Lula da Silva told the BBC that in the good years the rich countries had talked a lot about free trade and the market. Now they had created a crisis, they should not turn to the protectionism that had so often held the world back.