BERLIN - Germans voted in a national election Sunday with Angela Merkel favourite to win a second mandate to lead a country hit by the global recession and at odds over its military role in Afghanistan.

Final surveys indicated the conservative Merkel was a shoo-in for four more years as chancellor, as voters reward her for guiding Germany calmly through its worst downturn since World War II.

But she may not get the business friendly coalition partner she wants coming out of the election.

Frank-Walter Steinmeier, leader of the centre-left Social Democrats (SPD) who have been in a "grand coalition" with Merkel for four years, has failed to dent the huge popularity of Forbes magazine's most powerful woman on the planet, but a late surge has left Merkel's coalition hopes on a knife-edge.Profile: Steinmeier background

"I am always optimistic," she told the mass-circulation Bild am Sonntag newspaper.

Security across Germany has been tight in the run-up to election day following a string of threats from Islamic militants, including Al-Qaeda chief Osama bin Laden, warning of attacks over Germany's presence in Afghanistan.

A close election result in 2005 forced Merkel's Christian Democrats (CDU/CSU) into a coalition with traditional rivals, the SPD.

Four years of loveless left-right government later, Merkel wants to ditch the SPD and replace it with the business-friendly Free Democrats (FDP), a party seeking small government and lower taxes.

Early in the campaign, both parties looked on course to attract enough votes to create a new coalition, but surveys last week suggested that the race had narrowed, with as many as a quarter of voters still undecided.

If Merkel and the FDP fail, the result will likely be another grand coalition.

"Voters will decide tomorrow how quickly we get out of this crisis," Merkel told a final rally on Saturday. "We are fighting for the German jobs of the future."

But in her second period in charge of Europe's biggest economy, the pastor's daughter from the former communist East Germany, known as "Angie", faces daunting challenges.Profile: Merkel background

Unemployment is forecast to shoot higher, and everything from health care to education to Germany's bloated social security system are in dire need of reform. German public finances are in tatters and its population ageing fast.

Abroad, Merkel's main challenge is set to be Afghanistan, where Germany has around 4,200 troops as part of a NATO force ensnared in the eighth year of an ever bloodier struggle with insurgents.

The mission, opposed by most German voters, may become a major domestic headache for Merkel if violence continues to worsen in the north of the country where Germany's soldiers are based.

Germany has never suffered an attack by Islamic extremists, but authorities fear that it is only a matter of time, with several suspected plots uncovered and Internet warnings a regular occurrence, including from German-born Muslims.

With all of the main parties in the Bundestag lower house supporting the deployment, with the exception of the far-left Die Linke, the Afghan mission has failed to register as much of an issue in this election campaign.

But the war may become a battleground in the next parliament, particularly if the SPD finds itself in opposition with new leadership.

If there is not sufficient effort to build up the Afghan army and police, "the US will have a second Vietnam, and Germany its first," the Berliner Zeitung daily said in an editorial last week.

Troops in Afghanistan have already registered their votes by postal ballot, while back home polling stations opened at 0600 GMT with good weather forecast.

The first exit polls were due at around 1600 GMT.