skeletons
(File photo) The remains were found close to the site of an old church Getty

A mass grave containing the bodies of at least 90 people has been uncovered at a site in central Madrid.

The gruesome discovery was made during the construction of a new theatre in the Spanish capital.

The remains, which were found in an historic district that has special government protection, have been exhumed.

It is believed the bodies are from the 17th century and belong to the Church of Desamparados, which formally occupied the site, reports Euro Weekly News.

It is thought the bones were placed there after being moved from the tombs of the adjoining church. Bones were usually cleared from church tombs once tombs were filled.

The skeletons have been passed on to an anthropologist to determine the possible causes of death, along with their sexes and ages. They will then be taken to a local archaeology musuem.

Archaeologist Paloma Sobrini told El Pais: "It's about knowing if the deaths occurred due to natural death, if it's women, children.

"[The find] has surprised us because of its size."