Police were also called to investigate the collapse of the pillar which was part of an external pergola at the house of Loreius Tiburtinus in the centre of the popular tourist site.
News of the collapse was announced by the Special Archaeology Superintendent of Naples and Pompeii and the site was immediately closed to the public.
The House of Loreius Tiburtinus is famous for its extensive gardens and outdoor ornamentation, in particular its Euripi, fountains that feature many frescoes and statuettes. The frescoes portray the myths of Narcissus on one side of the fountain and Pyramus and Thisbe on the other in a garden full of fruit trees and other plants. At the end of November, the United Nations cultural agency UNESCO and the Italian government agreed to join forces to restore rain-damaged Pompeii after several recent collapses.
UNESCO said it would work with Italy over the next nine months to rebuild villas and other parts of the famed Roman site that have collapsed over the last year.
Under the deal, UNESCO said it would provide expert advice to the Italian government on how to upgrade conservation.
Last November there was a collapse in the House of the Gladiators which drew criticism from UNESCO and the European Union.
It was followed soon after by a collapse at the famed House of the Moralist, spurring further criticism from international conservation groups.
In October there were another three minor cave-ins, including one at the House of Diomedes, after a fresh bout of heavy rain and an outcry when an eight-square metre section of a wall fell near the Nola Gate.
Pompeii was destroyed when a volcanic eruption from nearby Mount Vesuvius buried the city in ash in 79 AD and it now attracts more than two million visitors a year.
Polemics about looting, stray dogs, structural decay and poor maintenance have dogged Pompeii in recent years.