The world's largest beer festival opened with a pop Saturday as the first keg was tapped at Munich's Oktoberfest, a 16-day extravaganza of lederhosen, oompah music and millions of ales.

With the traditional cry of 'O'zapft is' ('The keg is tapped') at midday, Mayor Christian Ude cracked open the first barrel and handed a foamy 'Mass' (litre-sized glass) to a grateful Horst Seehofer, Bavaria's state premier.

A steady drizzle did not seem to put the party-goers off as long queues formed around 8:00 am (0600 GMT) outside the bigger beer tents, two hours before the massive halls were to open and well before the suds began to flow.

American students Olivia Dassler, 19 and Brittany Cowan, 20, originally from California, came all the way from their university in Florence, Italy for the unique Oktoberfest experience.

"Everyone that comes abroad, it's the first thing they book, the first thing they want to do," said Cowan, resplendent in a pink dirndl, a long-pleated smock worn with low-cut blouse.

"We're even thinking of coming back next weekend if we have a good time. We've heard such good things about Oktoberfest."

Her friend Olivia, also dressed up to the nines in matching pink dirndl, said the traditional dress was a must.

"I've never been to Germany before, so when I think of Munich that's what I think of, the outfits. I know it's kind of stereotypical but they're so cool," she said.

More than six million revellers from around the world were expected to attend this year's festival and slurp between them around seven million litres of the amber nectar in one of the 35 giant beer tents stretching over 26 hectares.

To wash it down, punters will gobble literally tens of thousands of giant soft pretzels, pork, dumplings and other traditional Bavarian delicacies. Last year, drinkers worked through 118 oxen and 53 calves.

Bavarian pilot Andreas Maffey, 33, said he was proud to be a part of the festival.

"We have the privilege and the luck to have the world's biggest festival on our doorstep," he said.

"I reserve a table every day during the Oktoberfest but I can't come every day -- my liver wouldn't take it," he joked, adding he expected nonetheless to consume "around eight" litre-sized glasses.

Although the Oktoberfest started life 202 years ago, this year's event is the 179th edition as the party was cancelled during two world wars, two cholera outbreaks, Napoleon's invasion of Bavaria and the hyperinflation of the 1920s.

While not as extreme as the 1920s, campaigners have been up in arms this year about what they see as extravagant rises in the price of beer, which this year will set visitors back between 9.10 euros ($11.80) and 9.50 euros.

The price has risen by 43 percent over the past decade and a movement is underway to cap the price of beer at just over seven euros and to limit the annual rise.

As every year, tourists from around the globe come to observe a particular slice of German culture, wondering at everything from the music to the clothes.

Men wear the traditional Tracht - lederhosen (leather shorts) and embroidered braces - while women don dirndls.

Bavarian tradition dictates that deerskin lederhosen are the best because they stretch to accommodate an expanding beer belly.

The festival 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.

The format has been exported around the world and versions of the festival can be found as far afield as China, Brazil, Canada, the United States, Russia and Australia.

This year's event runs until October 7.

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