The Vatican's former ambassador to the Dominican Republic, who had been charged with sexually abusing children in the Caribbean country, has died as he awaited trial.

Jozef Wesolowski, 67, was found dead in the Vatican room where he has been held on house arrest, according to a statement from the Vatican.

Initial checks "indicated that the death was from natural causes", a press statement said.

It said the Vatican prosecutor ordered an immediate post-mortem and that Pope Francis was informed.

Wesolowski had been due to go on trial in a Vatican tribunal on July 11 for allegedly causing grave psychological harm to victims and possessing child pornography.

But on the morning of the hearing, he was admitted to intensive care because of an unidentified "sudden illness". No new trial date was made public and the presiding judge had adjourned the trial indefinitely.

Wesolowski was previously defrocked under the Vatican's canon law procedures but was facing possible jail time if convicted in its civil tribunal.

The trial had been seen as a high-profile way for Pope Francis to deliver on pledges to punish high-ranking churchmen involved in sex abuse of minors, either by molesting children or by systematically covering up for priests who did.

Recent changes to the Vatican legal code under Francis' leadership allowed prosecutors to broaden their case against Wesolowski.

Charges included possession of what prosecutors described as enormous quantities of child pornography on his two computers, including after Wesolowski was recalled to the Vatican in 2013 following the emergence of rumors that he sexually abused shoeshine boys near the waterfront in Santo Domingo, the capital of the Dominican Republic.

Wesolowski was the first such high-ranking Vatican prelate to be criminally charged at the Holy See for sexually abusing minors.

The case was particularly delicate because Wesolowski was a direct representative of the pope and had been ordained as a priest and bishop by his fellow Pole, the late pope John Paul II.