Pope Benedict XVI has arrived for the last audience of his pontificate in St Peter's Square on the eve of his historic resignation as leader of the world's 1.2 billion Catholics.

Tens of thousands of pilgrims gathered at the Vatican on Wednesday to bid a final farewell to the 85-year-old pope who abruptly cut short his pontificate by declaring he was too weak in body and mind to keep up with the modern world.

The Vatican said 50,000 people had obtained tickets for the event but many more might come, and city authorities were preparing for 200,000, installing metal detectors in the area, deploying snipers and setting up field clinics.

No parking has been allowed in the zone since 10pm local time on Tuesday, and cars were to be barred entirely from 7:00am on Wednesday.

Al Jazeera's Barbara Serra, reporting from the Vatican, said large numbers of people were already waiting for the Pope to deliver his final address.

"St Peter's Square has been turned into some kind of theatre. There's 50,000 seats, so that's the people that have booked their tickets and then there are others that will just come," she said.

"We are expecting many, many more to come. All the streets around St Peter's Square have already been blocked off. We have already seen groups of people making their way there, trying to get those seats for which tickets haven’t been sold ... People are making sure they are not going to miss what is for them - and for this Pope - obviously a historic day." 

First papal resignation

The weekly audience, which is exceptionally being held in St Peter's Square because of the numbers expected, is to begin at about 10:30am local time (09:30 GMT). It usually lasts almost an hour with a mixture of prayers and religious instruction from the pope.

Benedict will be the first pope to step down since the Middle Ages - a break with Catholic tradition that has worried conservatives but kindled the hopes of Catholics around the world who want a breath of new life in the Church.

Rome has been gripped by speculation over what prompted Benedict to resign and who the leading candidates might be to replace him.

Rumours and counter-rumours in the Italian media suggest cut-throat behind-the-scenes lobbying, prompting the Vatican to condemn what it has called "unacceptable pressure" to influence the papal election.

Campaign groups have also lobbied the Vatican to exclude two cardinals accused of covering up child sex abuse from the upcoming election conclave.

The Vatican has said Benedict will receive the title of "Roman pontiff emeritus" and can still be addressed as "Your Holiness" and wear the white papal cassock after he officially steps down at 1900 GMT on Thursday.

Source: Al Jazeera And Agencies