Thousands of people have packed the square outside the Pope John Paul II's window to pray for the pontiff as he clings to life.

Vatican officials held a special prayer service in St. Peter's Square, where one official said "Christ is opening the door to the pope today."  Earlier Mass was celebrated in a Rome basilica.

The Vatican said Friday the pope's condition has deteriorated and his breathing has become shallow.  It says he has kidney problems, and increased respiratory and circulatory difficulties.

A visibly upset Vatican spokesman, Joaquin Navarro-Valls, said earlier Friday the pope received Vatican officials, asked for scriptures to be read, and celebrated Mass.

The Vatican said the pontiff had suffered a "cardio-circulatory collapse" after developing a high fever from a urinary tract infection.  Officials said the pope wanted to remain at the Vatican, instead of going to the hospital.

The 84-year-old pontiff suffers from Parkinson's disease and a number of other health problems.  He underwent a procedure in February to ease breathing difficulties. 

Some information for this report provided by AP, AFP.