Thousands of mourners packed a Shanghai square Saturday to bid farewell to "underground" Catholic Bishop Joseph Fan Zhongliang whose faith, they said, led him to endure decades of suffering at the hands of China's ruling Communist Party.

Fan, who was imprisoned for much of the last two decades and spent his final years under house arrest, died last Sunday at the age of 97 after several days of high fever, according to the US-based Cardinal Kung Foundation, a Roman Catholic organisation.

China has a state-controlled Catholic Church, which rejects the Vatican's authority, as well as an "underground" church. Experts estimate that there are as many as 12 million Catholics in China, split roughly evenly between the two churches.

"I came here to bid farewell to our bishop," said a woman in her 60s who gave her name only as Clare and who was among a throng of mourners gathered outside the funeral home where Fan's body was laid out.

"He had kept loyal to the Lord throughout his life and endured great suffering. I have great respect for him," she said of Fan, who was appointed bishop of Shanghai in 2000 by Pope John Paul II.

In the square outside the funeral home, a large screen displayed photos of Fan while mourners sang, prayed and listened to a man narrating the bishop's life story.

As the service got underway, it relayed scenes from inside the funeral home: Fan's body was laid out in the centre, flanked by mourners and clergy in red-and-white robes. A large photo of Fan adorned the hall, surrounded by flowers.

Chinese authorities had turned down a request from worshippers to hold Fan's funeral service at Shanghai's main Catholic cathedral, the Cardinal Kung Foundation said.

- 'Forbidden' from pastoral duty -

Fan was ordained a priest in 1951 and spent more than two decades in jail and labour camps. His appointment as bishop of Shanghai in 2000 was rejected by China's state-run church.

"Bishop Fan was forbidden to carry out his pastoral duty as the government put him under house arrest almost immediately -- a sentence that he served until the day he died," Joseph Kung, president of the foundation, wrote in a statement.

China's Communist regime broke ties with the Vatican in 1951, and although relations have improved in recent years as the country's Catholic population has grown, they remain at odds over which side has the authority to ordain priests.

Shanghai is considered an important diocese given the city's historical ties to the Catholic Church -- it was home to Xu Guangqi, one of the most prominent converts secured by 16th-century Italian missionary Matteo Ricci.

The long-serving bishop of Shanghai's state-run Catholic Church, Aloysius Jin Luxian, died last year at age 96.

It remained unclear Saturday whether authorities had responded to a request from overseas and underground Chinese Catholics to allow Jin's successor, Thaddeus Ma Daqin, to preside over Fan's funeral.

Ma was stripped of his title after he dramatically split with China's state-run church at his installation ceremony last July and has since been under house arrest.