Custodians found that a two-metre wall of an ancient shop in the ruined city - which had recently been restored - had collapsed under the weight of another wall that crumbled onto it.
It followed the discovery Sunday that parts of an archway in the temple had fallen off and a wall in the necropolis - the biggest in the ancient Roman city - had tumbled down.
The areas affected have been closed the public.
Italian Culture Minister Dario Franceschini has called a meeting this week to assess the damage and progress made in an EU-backed project to restore the archaeological site.
"The news of these collapses comes at a time in which there is an unprecedented vacuum in the management of Pompeii," said Antonio Irlando from the Cultural Heritage Observatory, a non-governmental group that follows work on Pompeii.
"For every collapse that is reported, there are another nine that do not make news," he said, calling the state of the ancient site "dramatic".
Conservation workers last year began a €105 million makeover of the UNESCO World Heritage landmark, funded by the European Union to the tune of €41.8 million.
Officials in February reported the completion of the first project under the plan - the restoration of the frescoed House of the Cryptoporticus - but the project has been badly delayed by bureaucracy.
The project is seen as crucial to the survival of Pompeii after a series of collapses at the 44-hectare site in the shadow of Mount Vesuvius - the volcano that destroyed the city in 79 AD.