Voters are going to the polls in the US mid-term elections which will see a new House of Representatives and a third of the Senate elected.

President Barack Obama’s Democratic Party is expected to lose its majority in the House of Representatives, but may hold on to the Senate.

Republicans hope to capitalise on voter discontent with the economy.

Voting will end when the last poll closes in Alaska at 0000 EDT (0400 GMT).

Up for election are all 435 seats in the House (the lower chamber of Congress), 37 of the 100 seats in the Senate, governorships of 37 of the 50 states and all but four state legislatures.

The Republican Party needs to gain 39 seats to win control of the House and 10 to take over the Senate.

Presidential broadcasts

Opinion polls predict the Republicans will seize the House, while the race for control of the Senate is likely to be tighter.

In addition, voters will decide on some 160 measures on the ballots in 37 states ranging from marijuana legalisation in California to a referendum in Oklahoma on forbidding judges from using Islamic Sharia law in rulings.

If Californians decide in favour of legalising marijuana possession for personal use, it will put their state at odds with federal law.

At one polling station in Arlington, Virginia, there has been a steady trickle of voters since 0700, says the BBC’s Claire Bolderson.

The area is a staunchly Democratic bastion with a Republican minority, says our correspondent.

All of those interviewed said government spending was their main concern, talking about the need for more “fiscal responsibility” in Washington.

In an election day e-mail, Mr Obama congratulated his supporters for delivering health insurance reform after almost a century of thwarted efforts by presidents and lawmakers.

“No longer will a mother have to choose between cancer treatment and a mortgage payment – because of you,” he wrote.

“Because of you, we reined in Wall Street. Because of you, the economy is growing again… I need you to make sure your voice is heard.”

Mr Obama also continued with a second day of radio interviews on Tuesday, placing calls from the Oval Office to radio stations across the US to help rally Democratic support in favor of an post-recession, economic revival.

“Are we taking the steps now to move us in the right direction, or are going to go back to the policies that got us into that mess in the first place?,” the president asked the audience of one Los Angeles radio station.

The president placed calls to several other stations across the US with significant African American audiences.

Meanwhile, Republicans are buoyantly forecasting a new era of divided government.

“We’re hoping now for a fresh start with the American people,” said Republican National Committee Chairman Michael Steele.

If Republicans take control in either the House or Senate, President Obama could face difficulty when attempting to enact his proposals during the next two years. A Republican victory could also force Mr Obama to fight off attacks on health care legislation and bills already signed into law.

Republicans are riding high in opinion polls, buoyed by discontent over unemployment running near 10%, slow economic growth and a burst housing market bubble that has seen many Americans lose their homes.

The party has also gained from the backing of the populist Tea Party movement, which has given voice to conservative grassroots opposition to Mr Obama and the Democrats’ economic stimulus programmes and healthcare overhaul.

In several areas, the Tea Party, with the backing of former Alaska governor and 2008 Republican vice-presidential candidate Sarah Palin, has managed to replace establishment Republican candidates with more conservative figures.