According to official sources, more than 30,000 Pakistani soldiers were deployed in parts of South Waziristan, a possible hide-out of Osama bin Laden and a base for jihadists bent on spreading terrorism in the world.
Sources also said the operation was expected to last around two months.
Pakistani army spokesman Maj Gen Athar Abbas confirmed on Saturday evening that a full-fledged ground operation was under way and said that it aimed to "uproot" the Pakistani Taliban.
The United Nations has said it is preparing to help civilians who are fleeing the region. Up to 1,50,000 civilians have already left in recent months after the army made clear it was planning an assault.