Democrats surged to a 56-seat majority in the US Senate, wresting five seats from the Republicans as voters approved a mandate for change with the election of Barack Obama as president.

Leading lawmakers hailed their expanded control of the Senate as the start of a new chapter in history, even as they fell short of a 60-seat margin that would have given them power to block Republican delaying tactics.

`Tonight, the American people have called for a new direction. They have called for a change for America,` said House speaker Nancy Pelosi, who promised progress on rebuilding the economy and improving education and healthcare.

Prior to Tuesday`s vote, Democrats held 49 seats in the 100-member Senate but enjoyed a relative majority thanks to the support of two independents.

Optimism among Democrats ran high as massive voter turnout, economic woes and disdain for Republican policies fueled victories in key races in Virginia, New Hampshire, North Carolina, Colorado and New Mexico.

Democrats won 17 of the 35 Senate seats up for grabs, while Republicans took 14. Four races were still undecided at 0630 GMT.

The House of Representatives also swelled in the ranks of Democratic blue with 25 seats going to members of Obama`s party, driving up their previous 36 seat majority in the 435-member chamber.

The wins gave Democrats their second significant boost since the 2006 elections, when they gained 30 seats in the House and six in the Senate, wrenching both lawmaking chambers from the Republicans.

`It`s a great night for the United States Congress. And it`s a great night for the United States of America,` said House Majority leader Steny Hoyer, whose party is eager to use its new leverage with Obama as commander-in-chief.

`The days of obstruction are over,` he said. `And in a bipartisan way we in the Senate and my colleagues in the House will work together to turn America in the right direction after eight long years.

The first Senate win of the evening went to Democrat Mark Warner in Virginia, elected to fill the seat being vacated by retiring Republican John Warner, who is no relation.

In the northern US state of New Hampshire, Democrat Jeanne Shaheen unseated Republican John Sununu, while in the western state of New Mexico, Democrat Tom Udall won the seat left behind by retiring Republican Pete Domenici, who was first elected in 1972.

North Carolina tipped to Democrat Kay Hagan after a tense race with incumbent Republican Elizabeth Dole, whose campaign faces a defamation lawsuit over an ad it ran linking Hagan to `Godless Americans,` an atheist political action committee.

`What we were able to accomplish in a little more than a year is a testament to how hungry people are for a change,` Hagan said in her victory speech.

`So much has gone off course for the last eight years, and it`s going to take all of us working together to get it turned around again.`

However, a symbolic race in Kentucky was narrowly won by Republican Senate majority leader Mitch McConnell, who survived to win his fifth term with 51 percent of the vote, depriving Democrats of what would have been a major coup.

`Tonight marks the end of the one of the most exhilarating elections in US history. It also marks a beginning,` said McConnell.

`Regardless of one`s political party, election day is always a moment of optimism and hope.`

Republicans lost control of the Senate and House two years ago, and braced for further losses amid a public backlash over the widening financial crisis and discontent with outgoing President George W. Bush.

Approval ratings for Congress have sunk to historic lows -- just 15 percent according to a recent CBS poll -- but voters blame the Republican administration for the financial crisis, despite the Democratic majority among lawmakers.

Republicans have argued that liberal policies will be allowed to go unchecked with Democrat running the White House and more Democrats pouring into the House and Senate.

One remaining key battleground was Minnesota where comedian Al Franken is aiming to conquer the Senate seat from Republican Norm Coleman in one of the costliest races in the country -- with more than 32 million dollars raised for the campaigns.

In yet another tight race, Democrats in Alaska aimed to take advantage of veteran Republican Senator Ted Steven`s guilty verdict in a corruption trial last month. However, incumbents traditionally have higher chances of winning re-election than newcomers.