BERLIN - Voters in Germany's most populous state strengthened a center-left regional government which Chancellor Angela Merkel's conservatives had portrayed as irresponsibly spendthrift, and inflicted an embarrassingly heavy defeat Sunday on the German leader's party, projections showed.

The center-left Social Democrats and Greens - Germany's main opposition parties - won combined support of about 51 percent in the election in North Rhine-Westphalia state, according to ARD television projections based on exit polls and early counting.

That would be enough to give them a majority in the state legislature, which they narrowly missed in the last regional election two years ago. Meanwhile, support for Merkel's Christian Democrats was seen dropping to 26 percent from more than 34 percent, their worst showing in the state since World War II.

The outcome boosted Germany's center-left opposition, and gave food for thought to Merkel's conservatives, as the country looks toward national elections due late next year and the chancellor grapples with Europe's stubbornly persistent debt crisis.

The pro-market Free Democrats, Merkel's struggling partners in the national government, performed respectably, polling more than 8 percent to buck speculation that they might fail to win seats - a result that may help stabilize the party.

The state government of popular Social Democratic governor Hannelore Kraft had been favored to win, particularly after a much-criticized and gaffe-prone campaign by conservative challenger Norbert Roettgen, Merkel's federal environment minister.

"This is a crashing defeat for Mrs. Merkel and her minister," said Andrea Nahles, general secretary of the Social Democrats, whose share of the vote rose to nearly 39 percent from 34.5 percent. The success, she said, gave her party "tail wind."

"The defeat is bitter, it is clear and it really hurts," a crestfallen Roettgen said minutes after polls closed, announcing that he would give up the leadership of the Christian Democrats' local branch.

"This is, above all, my personal defeat," he said.

About 13.2 million people were eligible to vote in the western state, a traditional center-left stronghold which includes Cologne, Dusseldorf, and the industrial Ruhr region.

North Rhine-Westphalia voted three years ahead of schedule after Kraft's minority government narrowly failed to get a budget passed in March. Merkel said then that it offered an opportunity for the region to elect a government that wouldn't take on more debt.

While national polls show Germans support Merkel's pro-austerity stance in Europe, prominent Christian Democrat Peter Hintze said Sunday that voters in North Rhine-Westphalia viewed regional budget deficits as an "abstract theme."

Sunday's election - unlike North Rhine-Westphalia's last vote in 2010 - won't change the national balance of power.