BERLIN (Reuters) - The German state of Bavaria plans "emergency measures" to slow arrivals of asylum seekers, including sending some back to neighboring Austria, state premier Horst Seehofer said, directly challenging Chancellor Angela Merkel over the crisis.

Seehofer says more than 225,000 refugees have arrived in his southern state in less than five weeks and authorities are stretched beyond the limit to house and care for them all.

The Bavarian cabinet will meet on Friday to agree the measures, although legally the state cannot send back refugees as this would be a matter for the federal government in Berlin, where Merkel has refused to cap the number of arrivals.

Seehofer told Bild newspaper that the meeting would examine how to integrate refugees. "On top of that will come specific self-defensive measures to limit migration, such as sending back people to the border with Austria and the immediate transfer of newly arrived asylum seekers within Germany," he said.

Vienna warned of the risk of violence if the government in Bavaria, the main entry point into Germany for asylum seekers moving north through the Balkans and Austria, went ahead with the plan.

"If refugees who wish to remain in Germany are sent back to Austria, then you have to expect riots ultimately," said Interior Minister Johanna Mikl-Leitner.

She was speaking after raising the issue with German Foreign Minister Frank-Walter Steinmeier and Interior Minister Thomas de Maiziere at a European Union meeting in Luxembourg. Both "are naturally very worried", she said.

Although in the same conservative parliamentary bloc, Seehofer is at loggerheads with Merkel on handling the refugee crisis as he insists that limits on numbers allowed into Germany are needed.

Merkel has made clear she will not introduce a refugee cap. "There will not be an entry stop," she told ARD television late on Wednesday.

Her Social Democrat (SPD) coalition partners have also dismissed the idea of limits. Vice chancellor and SPD chief Sigmar Gabriel said it was unrealistic to close the borders.

Story continues

"We do not have a drawbridge we can lift," he said, adding refugees are fleeing Syria due to the dramatic situation there.

"Closing the borders - someone would have to tell us how that's supposed to work. Are we going to have the army there, with bayonets at the ready? Nobody would do that," he said, adding the causes of flight, hunger and misery had to be fought.

The refugee crisis is taking its toll on the popularity of Merkel's conservative Christian Democrats (CDU) and also their Bavarian sister party, the Christian Social Union (CSU), which Seehofer leads.

(Reporting by Madeline Chambers and Tom Körkemeier; Writing by David Stamp; Editing by Alison Williams)