Munich (Germany) (AFP) - Munich tapped the keg Saturday on the world's biggest beer festival, Oktoberfest, with six million revellers expected just as the German city is grappling with a record refugee influx.

The celebration of traditional Bavarian culture with its oompah music and beloved frothy beverage kicked off when Mayor Dieter Reiter opened the first beer barrel with two mallet blows and offered a toast to a "peaceful" Oktoberfest.

While the mood in town in the run-up to the 16-day event remained undauntedly festive, Munich had to plan its huge annual party just as it became a flashpoint of Europe's migrant crisis.

More than 20,000 people, many of them Syrians, Afghans and Iraqis fleeing war and persecution, have descended on the city of 1.4 million on each of the last two weekends.

They met with an overwhelmingly positive reception from the public, including an outpouring of donations.

But the number of arrivals dropped markedly in the last week to a few hundred per day due to border controls implemented from Sunday at the request of Bavarian authorities, who had described themselves as overwhelmed by developments.

Migrants are now being picked up at the Austrian border and put on buses and trains to other German regions, most now bypassing Munich, where some 6,000 asylum-seekers are housed in temporary shelters.

"The situation is more relaxed than it was in recent days," federal police spokesman Wolfgang Hauner said.

Bavarian Interior Minister Joachim Herrmann, who had warned of a potential culture clash between Muslim refugees and beer-swilling merrymakers, appointed a migration crisis team on the eve of the event.

Police have deployed 500 officers at the sprawling Wiesn fairgrounds, and mounted a security operation at the main railway station to keep drunken party-goers separate from arriving migrants.

- Accommodating beer bellies -

Visitors from around the world wear the traditional Tracht, sometimes hastily bought at a vendor's stand: lederhosen (leather shorts) and embroidered braces for men and dirndls, pleated smocks worn with low-cut blouses, for women.

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Both are designed to expand to accommodate an expanding beer belly.

Mexican Gabriel Estrada, 49, arrived early Saturday in warm and sunny weather decked out in full Bavarian regalia along with his wife and 22-year-old son.

An engineer for luxury automaker BMW, Estrada said that Munich residents have largely made his family feel welcome during their three-year stint in the city.

"We love the tradition here, everyone all dressed up -- it's a real people's party," he said.

But his wife Beatriz, 48, said that many in town seemed on edge over the refugee influx.

"There are a lot of scared people -- they don't know how things are going to go and worry there could be attacks," she said.

A far-right group planned an anti-refugee rally at the railway station at 1600 GMT.

A spokesman for the volunteers helping to process the new arrivals at the station, Colin Turner, said he expected the numbers to increase again dramatically after the event ends on October 4.

"They can't keep the border checks in place for ever," he said.

"Of course they redirected people so they wouldn't come during Oktoberfest but having them arrive on trains in larger groups to Munich actually helps us coordinate our assistance."

Although Oktoberfest began 205 years ago, this year marks the 182nd edition as the party was cancelled during two world wars, two cholera outbreaks, Napoleon's invasion of Bavaria and the hyperinflation of the 1920s.

Prices for a "Mass" or large glass of beer have soared in recent years and will now set drinkers back between 10 euros ($11.40) and 10.40 euros.

The event was originally held in October as the name suggests to celebrate a royal wedding but was brought forward by one month to take advantage of better weather.