GERMAN chancellor Angela Merkel's main challenger in September's election said his party will not be put off its stride by a deflating result in a state vote - and warned his conservative rivals against early celebrations.

Merkel's Christian Democrats easily beat challenger Martin Schulz's centre-left Social Democrats in Saarland state on Sunday.

A much tighter race had been expected after the Social Democrats were boosted in polls by nominating Schulz, a former European Parliament president, but a newcomer to national politics, in January.

The popularity of Saarland's conservative governor apparently trumped what has become known as the "Schulz effect".

However, Schulz said: "We have picked up support in the last few weeks, in Saarland too, and we are looking ahead.

"We're in it for the long haul - that message goes to those who are celebrating today, understandably from their point of view, but should not celebrate too early.

A deputy leader of Merkel's party said the Saarland win gives the conservatives "tail wind" for the upcoming elections, but refused to take anything for granted.

Armin Laschet told ZDF television: "Everything that was said about the Schulz train rolling over everything and changing everything didn't come true."

Laschet faces an uphill task to oust a centre-left government in North Rhine-Westphalia in May. It is Germany's most populous state and Schulz's home region.

He said: "We have tail wind, but we haven't won anything yet. It will be difficult."

In Saarland, the Social Democrats failed to win enough support for a new coalition with the hard-left opposition Left Party.

While a similar national alliance adding another left-leaning party might be Schulz's best hope of becoming chancellor, the prospect may also have turned off Saarland voters.

Schulz said it would be "not just wrong but negligent" to draw conclusions from that for other elections.