Updated: Thu Dec. 24 2009 18:31:10

The Associated Press

VATICAN CITY — A woman jumped the barriers in St. Peter's Basilica and knocked down Pope Benedict XVI as he walked down the main aisle to begin Christmas Eve Mass on Thursday.

The 82-year-old pope quickly got up and was unhurt, said a Vatican spokesman, the Rev. Ciro Benedettini.

Footage aired on Italy's RAI state TV showed a woman dressed in a red, hooded sweat shirt vaulting over the wooden barriers and rushing toward the pope before being swarmed by bodyguards.

Video shot by a witness showed the woman grabbing the pope's vestments as she was taken down, with Benedict seemingly falling on top of her.

The commotion occurred as the pope's procession was making its way toward the main altar and shocked gasps rang out through the public that packed the basilica. The procession came to a halt and security rushed to the trouble spot.

Benedettini said the woman who pushed the pope appeared to be mentally unstable and had been arrested by Vatican police. He said she also knocked down Cardinal Roger Etchegaray, who was taken to hospital for a check up.

"During the procession an unstable person jumped a barrier and knocked down the Holy Father," Benedettini told The Associated Press by telephone. "(The pope) quickly got up and continued the procession."

MaryBeth Burns from Paris, Texas, was about four people away from the woman who jumped the barriers and was filming the pope's procession as the commotion started.

"I'm really mad because I had a perfect shot lined up," she said. "I'm still shaking."

Burns, who was visiting Italy with her family on a religious pilgrimage for Christmas, said the security guards immediately pulled the woman to the ground and the pope tumbled with them.

Benedict lost his miter and his staff in the fall. He remained on the ground for a few seconds before being helped back up by attendants. At that point a few shouts of "viva il papa!" (long live the pope!) rang out, followed by cheers from the faithful, witnesses said.

After getting up, Benedict, flanked by tense bodyguards, resumed his walk to the basilica's main altar to start the Mass. He did appear somewhat shaken and leaned heavily on aides and an armrest as he sat down in his chair.

Few people who were watching the Mass on giant screens set up in a rain-soaked St. Peter's Square even knew that the pope had fallen, with many saying that either they weren't looking or had arrived too late.

Benedict made no reference to the incident as the service started. As a choir sang, he sprinkled incense on the altar before opening the Mass with the traditional wish for peace in Latin.

It was the second year in a row there was a security breach at the service. At the end of last year's Mass a woman who had jumped the barriers got close to the pope but was quickly blocked on the ground by security.

That woman too had a red sweat shirt, but Benedettini said it was not immediately known if the same person was behind Thursday's incident.

The latest incident was the first time a potential attacker came into direct contact with Benedict, and underscored concerns by security analysts who have frequently warned the pope is too exposed in his public appearances.

There have been other security breaches at the Vatican.

In 2007, during an open-air audience in St. Peter's Square, a mentally unstable German man jumped a security barrier and grabbed the back of the pope's open car before being swarmed by security guards.

Then there was the assassination attempt against Pope John Paul II by Turkish gunman Mehmet Ali Agca in 1981. John Paul suffered a severe abdominal wound as he rode in an open jeep at the start of his weekly audience in the Vatican piazza.

The pope is protected by a combination of Swiss Guards, Vatican police and Italian police.

Since the Sept. 11 attacks on the U.S., the Vatican has tightened security at events where the pope is present. All visitors must pass by police to get into the square, with some going through metal detectors or being scanned by metal-detecting wands.

In a similar incident to Thursday's, Italian Premier Silvio Berlusconi was attacked as he was greeting the crowd at a political rally earlier this month. A man with a history of psychological problems hurled a souvenir statuette at the politician, fracturing his nose and breaking two of his teeth.

Benedict celebrated this year's Christmas Eve Mass two hours earlier than the usual midnight starting time in a move by the Vatican to ease the pontiff's busy holiday schedule.

In his homily, delivered unflappably after the incident, Benedict urged the world to "wake up" from selfishness and petty affairs, and find time for God and spiritual matters.

"To wake up means to leave that private world of one's own and to enter the common reality," Benedict said. "Conflict and lack of reconciliation in the world stem from the fact that we are locked into our own interests and opinions, into our own little private world."

Benedict's next scheduled appearance is at noon on Christmas Day, when he is to deliver his traditional "Urbi et Orbi" speech (Latin for "To the city and the world") from the basilica's balcony.