Yesterday's vote saw Merkel's party seize the state from the Social Democrat (SPD) opposition and delivered her fresh momentum as she gears up to make her bid for a fourth term as leader of Europe " s biggest economy in September " s national election.
CDU won 33 percent of the vote, gaining around 6 percentage points since the last election, while the SPD won about 31.5 percent, having lost nearly 8 percent point since 2012.
Exit polls broadcast just after polls closed at 6 p.m. showed the Christian Democrats winning 34.5% of the vote, up from 26% in the last election in 2012. "We will continue fighting, the result will come on 24 September".
So although the concrete issues that shaped this election were primarily regional - such as schools, transport and security - this state also matters nationally. Ms. Kraft announced that she was stepping down as the Social Democrats' regional leader.
The nationalist Alternative for Germany won 7.4%, giving it seats in its 13th state legislature. Earlier this year, the CDU also won the elections in the state of Saarland. But that failed to translate into votes in the last two state elections, when the CDU won comfortably. She said she took full responsibility for her party's defeat in Sunday's election. "It's sad we lost so many districts".
The industrial state has been governed by a center-left coalition of the SPD and the Greens since 2010, with the Social Democrat Hannelore Kraft serving as state premier.
Martin Schulz said the loss in the state, Germany's most populous and regarded as a centre-left stronghold, was "a hard day for the Social Democrats, a hard day for me personally as well".
"I've heard the criticism of people who say 'you're nice, but you have to get more specific.' And that's what I plan to do", Schulz told CNN affiliate ARD.
The Free Democratic Party (FDP), Germany's liberals, fared significantly better with around 12 percent of the votes and are already claiming a comeback on the national political stage, according to its chairman Christian Lindner.
Merkel's CDU has won the three state elections held in Germany this year, and these wins are deemed to bode favorably for its performance in the national general elections in September. North Rhine-Westphalia is his home state and traditionally an SPD stronghold.
Support for the SPD surged in January when the party appointed former European Parliament president Martin Schulz as its leader, vowing to reverse unpopular labour market reforms that expanded the low-pay sector and boost welfare.
Martin Schulz on Sunday.
The AfD is now represented in 13 states across Germany.
A "grand coalition" would mirror Merkel's national government, in which the Social Democrats are the junior partners.