The 220 year-old Our Lady of the Immaculate Conception church in Milot, pictured in 2002, lost its dome in the fire. — AFP/VNA Photo

Port-au-Prince — A fire ripped through one of Haiti's oldest churches overnight, officials said on Monday, causing the dome of the UNESCO-listed world heritage site to collapse.

It was not immediately clear what caused the blaze at the Our Lady of the Immaculate Conception church in Milot, in the north of the country.

It caused the 30m diameter dome to collapse completely, said Patrick Durandis, director of the Institute for the Protection of National Heritage.

"The fire broke out towards 3am in an annex building, according to reports I received from someone at the someone at the scene."

"We were waiting for firefighters who were there but who unfortunately were not able to intervene for various reasons," he said.

Durandis said Milot had no electricity at the weekend, making the cause of the fire a mystery.

"We cannot blame a short circuit: there will have to be an investigation," he said, noting that the church had been closed anyway because of the coronavirus pandemic.

Some 20km south of Haiti's second city of Cap-Haitien, the chapel stands at the entrance to the large historic park known as the Laferriere Citadel, which has been classified as a UNESCO world heritage site since 1982.

"Given that it's a monument classified as a world heritage site, the restoration must be identical to the original, and since the funds are not available, there are a lot of questions about it," said Durandis.

"So I can say there's going to be a lot of work to get it back to what it was."

The royal chapel at Milot was built between 1810 and 1813 on orders from Henri Christophe, the hero of the Haitian war of independence who proclaimed himself king in 1811.

It was restored once before, in the 1930s, and underwent emergency repairs in 2018 to fill in large holes that had opened up in the roof of the dome. — AFP