Chinese officials are "still probing" the case of a bishop who resigned from the state-approved body overseeing Chinese Catholics immediately after his consecration went ahead without approval from the Vatican.
The Rev. Thaddeus Ma Daqin announced his decision on Saturday to applause from a packed church in Shanghai, Catholic media reported, citing church members.
Ma, an assistant bishop, was widely regarded as the likely successor to Shanghai Bishop Aloysius Jin Luxian, 95, who serves with the approval of the Vatican and the Chinese Patriotic Catholic Association.
"In the light of the teaching of our mother church, as I now serve as a bishop, I should focus on pastoral work and evangelization," Ma was quoted as saying.
"Therefore, from this day of consecration, it will no longer be convenient for me to be a member of the patriotic association."
Ma's consecration came as the Rev. Joseph Yue Fusheng was excommunicated by the Vatican for accepting Beijing's appointment as bishop of Harbin.
Ma was taken from Shanghai cathedral on Saturday shortly after his announcement by officials from the municipal religious affairs bureau.
He is now believed to be on "retreat" at a monastery outside the city.
"We are currently in the process of investigating the matter further," said Yang Yushen, spokesman for the Chinese Patriotic Catholic Association.
Yang said the Association had so far received no confirmation in writing of Ma's resignation.
"We don't know what he did, nor what his thoughts are," Yang said.
"No-one from our organization was present at the time of his consecration, so we don't know exactly which procedures were followed."
An employee who answered the phone at the Shanghai cathedral declined to comment.
"[Ma Daqin] is not here," the employee said. "This is the parish office, and we don't know anything here."
"We are just administrators, and we don't get involved with anything else," he said.
Asked if Ma had been "disappeared" by the authorities, he added: "How would I know that?" before hanging up the phone.
Relations between Beijing and the Vatican have come under repeated strain as China moves to ordain more and more of its own bishops without Vatican approval to meet the needs of a growing Catholic population.
The Vatican typically responds by excommunicating bishops who accept Beijing's consecration ceremonies, saying that only the Pope can appoint bishops.
Joseph Kung, spokesman for the U.S.-based Cardinal Kung Foundation, said Ma's resignation from the Association had been courageous.
"This is very good, very good," said Kung, whose organization follows China's "underground" Catholics, who worship without state approval and maintain loyalty to the Vatican. "It was also the correct thing to do."
"I wish every [Chinese] bishop would do the same thing."
He said bishops who resigned in a similar manner would likely be subsequently approved by the Pope.
"It makes no difference whether the Patriotic Association approves them or not."
Hong Kong's Justice and Peace Commission of the Hong Kong Catholic Diocese demonstrated on Wednesday to demand the release of Ma, whom they say is being held against his will.
"There are police outside watching him," said Shin-shin Koh, spokeswoman for the Commission. "His phone is temporarily switched off, or else it rings for a long time [with no answer.]"
"We don't really know if he is being held against his will, but...common sense dictates that he should have celebrated mass on Sunday," Koh said.
"He was unable to do this."
Around a dozen protesters shouted slogans, sang songs and prayed outside Beijing's representative office in the territory.
The state Church has ordained more than 190 bishops, according to official figures, although Catholic officials said recently that more than 40 of the country's 97 dioceses are without a bishop.
China's officially sanctioned Catholic Church has between five and six million members, while an underground church loyal to Rome has an estimated 10 million followers.
Reported by Bi Zimo and Wei Ling for RFA's Cantonese service, and by Xin Yu for the Mandarin service. Translated and written in English by Luisetta Mudie.