Security is tight in towns and cities throughout Pakistan in case the Taliban carry out revenge attacks.
Nearly all communications in the region were down after the Taliban destroyed a telecommunications tower at Tiarza, local officials said.
Aerial bombardments in the Makeen area, a stronghold of the Mehsud tribe and a key army target, were also reported by local officials and witnesses.
The ground operation comes after weeks of air and artillery strikes against militant targets in the region, which lies close to the Afghan border.
There is a huge army presence on the road between Tank and Dera Ismail Khan, says the BBC's Islamabad correspondent Shoaib Hasan, near South Waziristan.
The army has been massing troops near the militants' stronghold for months - ever since the governor of Pakistan's North West Frontier Province announced a ground offensive in South Waziristan on 15 June.
Pakistan's government has been under considerable pressure from the US to tackle militancy there.
North and South Waziristan form a lethal militant belt from where insurgents have launched attacks across north-west Pakistan as well as into parts of eastern Afghanistan.
South Waziristan is considered to be the first significant sanctuary for Islamic militants outside Afghanistan since 9/11.
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