OSLO - Oil-rich Norway's left-wing government was in danger of losing its Parliamentary majority despite breezing through the global recession, polls showed as voting started Sunday in a two-day ballot.

A TNS Gallup survey showed the three-party coalition led by Prime Minister Jens Stoltenberg's Labor Party was three seats short of keeping its hold on the Nordic welfare state's 169-seat legislature.

Stoltenberg would still have a chance of remaining in power with a minority government, because the centre-right opposition has been unable to muster a united front.

His top challenger is Siv Jensen and her right-wing populist Progress Party, which has gained support by calling for lowering Norway's famously high taxes and tightening immigration rules.

The two traded barbs in a debate in Oslo on Sunday, with Jensen saying repeated Labor governments have been unable to seal cracks in the welfare system, despite Norway's growing oil wealth.

Stoltenberg said voters shouldn't expect a "social-democratic paradise" by Tuesday and that the election was more about values and the country's direction.

"I believe that you won't build a social-democratic paradise by Tuesday because you've been at it since the war and you still haven't managed it," replied Jensen, whose role model is former British Prime Minister Margaret Thatcher.

Norway has escaped the financial crisis largely unscathed, partly by tapping into its oil and gas-fueled sovereign wealth fund - currently valued at more than 2.4 trillion kroner ($400 billion). Unemployment stands at 3 per cent - among the lowest in Europe.

Oil and gas pumped from North Sea platforms have made the fjord-fringed country of 4.8 million people one of the world's richest nations. But that wealth also presents a challenge for every sitting government.

Norwegians have high demands on public services, and routinely complain about shortcomings, such as bad roads and long waiting lists at public hospitals for non-emergency treatment.

The Progress Party has seen support surge in recent years with calls for spending more oil revenue at home, to lower taxes and improve infrastructure. It also wants more privatization in health care and education and stronger demands on immigrants to integrate into Norwegian society.

Immigration has skyrocketed by a factor of five since the early 1970s - more than 10 per cent of Norway's population is of foreign origin. In recent years the biggest groups of asylum seekers have come from Afghanistan, Iraq, Somalia, and Eritrea.

Still, the relative strength of the Norwegian economy has dampened concerns about immigration.

Polling stations in about 200 municipalities opened Sunday, though Monday was the main election day.

The TNS Gallup survey published Saturday by the TV2 network showed the centre-left bloc getting 82 seats, including 61 for Labor. Eighty-five seats are needed for a majority in Stortinget, Norway's parliament.

Progress - the biggest opposition party - got 39 seats in the poll, while the centre-right Conservatives, Christian Democrats and Liberals got a combined 48 seats. The Sept. 9-12 poll of 2,000 people had an error margin of 2 per cent.

Both the Christian Democrats and the Liberals have ruled out forming a coalition with the Progress Party, mainly because of disagreements over immigration.

There's been virtually no talk about joining the European Union, which Norwegian voters have rejected twice, and which on average has been more severely hit by the recession.

Eurostat figures show Norway's economy contracted 2.5 per cent in the second quarter, compared to a drop of 4.8 per cent in the 27-nation EU.

"There is no momentum for applying for membership now," said Erna Solberg, the pro-EU leader of the Conservatives.

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Associated Press Writer Ian MacDougall contributed to this report.