Either plague or famine was likely the cause of death of most of those buried, though the total number of skeletons interred is yet to be established.

The remains have been dated back to the Swedish era in Estonia, when large parts of the country were under Swedish rule from 1561 – and the whole country from 1645 – to 1710, during the Great Northern War.

That the skeletons have been dated to that period is thanks to artifacts found near the remains.

Archaeologist Keiti Randoja said: "We have discovered a Swedish-era brooch and a Swedish-era öre coin near the skeletons – likely dating them to the 17th century or early 18th century."

The excavation will not halt the reconstruction work on the bus stop itself, on Kaarli pst, in central Tallinn.

The area is known as the Püha Barbara kalmistu (St. Barbara's cemetery) and is close to the Kaarli kirik, a church built much later, in the 19th century.

"As of now we have found about 40 skeletons, but it is hard to estimate how many more there might be," Randoja went on.

"I believe the excavation could take another couple of weeks. It is impossible to predict accurately, however, since the bodies are buried in a haphazard way. We have identified the mass grave as dating back either to one of the famines or plagues of the 17th century, or to the Great Northern War period, in 1710," the archaeologist added.

Noting the significance of the find, Randoja added it was: "Highly important for Tallinn. Here, simpler folk were buried, generally Estonians, including residents of the suburbs plus poorer Estonian citizens,."

Heritage Protection (Muinsuskaitseamet) chief specialist Oliver Orro said that this is not the first time archaeological finds have emerged at the site.

He said: "Previously, skeletons have been discovered during the construction of buildings and the laying of utility lines in this area."

"Over 2,000 skeletons have been excavated and reburied at the inner-city cemetery in Tallinn during these earlier archaeological digs. It turned out that there was still a small strip of previously unexcavated ground, which is where the newly discovered burials were found," Orro continued.

While part of the bus stop reconstruction work on Kaarli pst has been halted due to the discovery, work has not completely ground to a halt, and passengers can still use the stop.

The archaeological dig is (see gallery) likely to continue for another fortnight.

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