Making history with a stroke of his pen, US President Barack Obama Tuesday signed into law sweeping reforms that will for the first time ensure health care coverage for almost every American.

"It is fitting that Congress passed this historic legislation this week for as we mark the turning of spring, we also mark a new season in America," Obama told a jubilant, packed audience at the White House signing ceremony.

"The bill I'm signing will set in motion reforms that generations of Americans have fought for and marched for and hungered to see."

Delighted lawmakers and guests cheered and whistled as the dream of generations finally came to fruition, and Obama made good on his campaign promise to overhaul America's costly, but creaking health care system.

Lawmakers voted 219-212 to approve the Senate-passed legislation late Sunday, using their majority to muscle the measure through, in face of a united Republican opposition.

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With a package of fixes still to be voted on, the overhaul is estimated to extend coverage to some 32 million Americans who currently lack it, bringing to 95 percent the proportion of under-65 US citizens with private insurance.

For the first time Americans will be required to buy insurance or face fines. The new law bans insurance companies from denying coverage to people with pre-existing conditions, from dropping clients who get sick or from setting lifetime caps.

It carries an initial 10-year price tag of 940 billion dollars, but would reduce the ballooning US deficit by 138 billion dollars through 2019 and 1.2 trillion over the following decade, according to official figures.

The historic signing came a century after then president Theodore Roosevelt first called for a national approach to US health care.

Vice President Joe Biden praised Obama for accomplishing something that has eluded American leaders for decades in a country where falling ill can lead to bankruptcy for those without coverage.

"You've made history. History is made when the leader steps up, stays true to his values and charts a fundamentally different course for the country." Biden said.

"Mr. President, you've done what generations of not just ordinary, but great men and women have attempted to do.

"You have turned, Mr. President, the right of every American to have access to decent health care into reality for the first time in American history."

Senior White House adviser David Axelrod said earlier that Obama had never been happier than late Sunday, when the House of Representatives passed the core of his plan.

"I haven't seen the president so happy about anything, other than his family, as long as I've known him and worked with him," Axelrod told CNN.

The Senate was expected this week to take up the changes and approve them separately, under rules that prevent Republicans from using a parliamentary tactic, the filibuster, to indefinitely delay and therefore kill the measure.

But Obama still has a hard sell defending the reforms ahead of the key congressional November elections with Republicans deeply angered by the legislation, which they say is too costly.

"Democrat leaders may have gotten their votes. They may have gotten their win. But today is a new day," said Republican Senate Minority Leader Mitch McConnell. "I have a message for our Democrat friends: 'Enough is enough'."

Obama's former rival for the presidency, Republican Senator John McCain, even told an Arizona radio station Monday that "there will be no (bipartisan) cooperation for the rest of the year."

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On Thursday, the US president will launch the first of a series of campaign-style events on the bill's behalf in Iowa, the state that propelled him on the road to the White House.

Overturning the plan was a mathematical impossibility in this election cycle as Republicans cannot win the two-thirds majority in the House and Senate needed to override Obama's veto.

But the attorneys general of at least 12 states said they will file lawsuits against the legislation after Obama signs the bill, and Idaho and Virginia have already passed laws preventing their residents from being forced to buy insurance.