(Reuters) -Brazil's biggest city is throwing open the doors of its main Carnival arena to hordes of rival fans this weekend, as more than 70,000 Argentines arrive for a World Cup match on Tuesday.

Sao Paulo officials laid out their game plan on Friday for the Argentine invasion, urging visitors to camp in designated areas and stay away from the stadium if they do not have tickets.

Caravans of Argentine cars, trucks and camper vans drove thousands of miles to descend on Rio's Copacabana beach for their team's opening game two weeks ago. Crowds are only growing as the month-long tournament advances.

Tens of thousands of Argentines also swarmed across the Brazilian border to the southern city of Porto Alegre this week. Half a dozen of them were arrested stealing tickets before the Wednesday match and one Argentine fan was shot in a bar fight, stoking worries about possible violence if Argentina meets Brazil in the championship match.

Brazil has already stopped more than 30 Argentines from entering the country due to their involvement with hooliganism in their national soccer league.

For the Tuesday game between Argentina and Switzerland, Sao Paulo officials played down security concerns, citing a strong track record from hosting four World Cup games so far.

"The main question for Argentina is the quantity of fans, many of whom do not have tickets to the game," said city hall spokesman Leonardo Barchini. He recommended neighborhood bars to those visitors. An official fan fest downtown has suffered overcrowding during some games.

The Interlagos racetrack at the south end of Sao Paulo will also serve as an Argentine campground over the weekend. The racetrack was the site of a legendary 1991 Grand Prix victory by Brazilian Ayrton Senna, who won the race with a failing gearbox and then collapsed from exhaustion.