The Rio de Janeiro Carnival 2012 is expected to attract its largest ever audience with organisers expecting 850,000 people over the five-day event - a 20 percent more than in 2011.

Rio officials said they were better prepared to keep the chaotic streets under some semblance of control, with more portable toilets, traffic guards and paramedics available and a new central command centre monitoring it all.

"We want revellers to be conscious that they can party but also care for the city's public spaces," the president of Rio's tourism department, Antonio Figueira de Mello, said.

Rio officials dispatched 80 mobile medical emergency units, 1,000 traffic guards and 15,000 toilets around the city and officials launched a campaign against urinating in public.

It will be seen as a trial run for the central command centre which will be tasked with making sure things run smoothly when Rio hosts many of the matches in the 2014 World Cup followed by the 2016 Olympics

The centre, which takes feeds from more than 500 cameras spread around the city, will monitor the routes of more than 400 roving street parties.

"There will be more than 5,000 city government workers involved in making this party go as smoothly as possible for cariocas [residents] and for the tourists," said Savio Franco, who runs the centre.

Rio Carnival 2012: Two Million Party on the Streets [SLIDESHOW]