Conservationists and city authorities locked horns in Estonia`s picturesque capital Tuesday, amid warnings that allegedly slapdash construction work has left a historic church at risk of collapse.

Leaked reports about damage to the Jaani Kirik -- or Saint John`s church -- in Tallinn`s touristic Old Town district sparked an angry reaction from Imre Tael, a leading Estonian restoration expert.

`It`s insane to keep the church open to public,` Tael told reporters.

Tael blasted the construction of an underground car park which he said has left the building`s fate hanging in the balance because builders allegedly failed to properly shore up the land.

`There is a clear danger it might collapse,` Tael said.

But Taavi Aas, the deputy mayor of Tallinn, who rushed to the site Tuesday, rejected the claims.

`The church was built on oak piles over an old moat, and the ground below it has been always soft. But we are sure at city hall that is no danger and that the church will not collapse,` Aas told AFP.

However, he acknowledged that cracks had appeared in the building.

Aas said that to calm public worries, city authorities had ordered the construction company to refill a hole near the church, and noted that work would be complete on Wednesday.

The Lutheran church was inaugurated in 1867, when Estonia was ruled by Orthodox Russia.

The building is particularly symbolic because it was the first place of worship in the capital to be funded and constructed by Estonians.

`People in the congregation have kept calm and kept coming to the services,` pastor Jaan Tammsalu told AFP.

`We do not want panic. But it is true the church floor has cracks in it and the area that has been dug out starts just seven metres (23 feet) from the entrance,` Tammsalu said.

One upside from the construction work is that builders uncovered a stretch of wall and a tower from Tallinn`s Medieval defences, which will be left visible in the car park.