VATICAN CITY (Reuters) - The Vatican has closed all of Italy's ancient catacombs normally open to the public because of the country's coronavirus outbreak.

Vatican official Monsignor Pasquale Iacobone said the decision was taken to protect guides who work in the restricted underground spaces as well as visitors.

Iacobone, secretary of the Pontifical Commission for Sacred Archaeology, told Reuters the grouping of visitors, small, narrow spaces and humid conditions in the catacombs made for ideal conditions for the virus to spread.

Italy is Europe's worst-hit country, with 17 deaths from the virus and 650 infections. The outbreak is focused on a small cluster of towns in the northern Lombardy and Veneto regions.

The catacombs are underground burial sites dating to the second century. The most famous and most visited are in Rome and consist of many kilometres of underground tunnels cut out of soft tufo stone.

The Vatican owns and administers them and numerous other Christian catacombs across Italy. About a dozen have been explored and opened to the public, including in Sicily, Tuscany and Sardinia.

"We hope to be able to reopen them as soon as possible but we really had no choice," Iacobone said.