71 year old Bishop Han Dingxiang spent nearly half his life in prison. He was cremated a mere six hours after his death on Sunday from unknown causes.
The US-based Cardinal Kung Foundation says none of his supporters was aware of any illness until local authorities summoned relatives to his bedside as he was dying in hospital.
Foundation president Joseph Kung asked: "What was the Chinese government afraid of, to cremate Bishop Han only six hours after his death, and at such an early hour at 5 o'clock in the morning?"
Kung urged the Vatican to open an inquest into Han's death.
Han, who was ordained bishop in 1989, was the underground Catholic bishop of Hebei's Yongnian diocese. His longest prison term was 19 years from 1960.
China Catholic bishop dies in custody (Sydney Morning Herald, 12/9/07)
Yongnian's underground bishop dies after two years in solitary confinement (AsiaNews, 11/9/07)
Ordination of Vatican approved China bishop goes ahead (CathNews, 4/9/07)
Pro-pope bishop arrested in China
Another Chinese bishop released (CathNews, 28/9/06)
Released Chinese bishop seeks reconciliation (13/9/06)
Chinese bishop released after 10 years in prison (CathNews, 28/8/06)
Holy See sends envoys to Beijing for secret talks (CathNews, 19/6/06)
China's first Catholic non-profit approved but arrests continue (CathNews, 4/8/06)
Pope declares diplomatic war with China (CathNews, 5/5/06)