Taleban militants and security forces in Pakistan's South Waziristan region have continued to exchange fire overnight, military officials say.
The military says troops are 'engaging' the militants
But precise casualty figures are not known because access to the region is restricted and information is slow to filter out, a BBC correspondent says.
Early reports say that troops have hit militant positions with artillery fire.
South and North Waziristan, adjoining the Afghan border, are strongholds of militants allied to the Taleban.
In the latest fighting, militants are reported to have responded to the army artillery attacks by firing missiles at security positions.
The BBC's M Ilyas Khan in Karachi says that there are reports of people moving out of the area and walking for miles to reach secure zones.
Our correspondent says the government has set up a temporary camp for displaced people in the Tank district of North West Frontier Province, where tents and food have been made available.
There are no reports yet of any people are sheltering there.
Mehsud tribesmen in Tank city called for a general strike on Wednesday, and have been trying to persuade traders from other tribes to join the strike.
Militant leader Baitullah Mehsud is based in South Waziristan and is accused of leading attacks by tribesmen on forts controlled by the army.
The authorities in Islamabad also accuse him of masterminding the murder of former Prime Minister Benazir Bhutto last month. Latest reports say that troops again exchanged fire again on Wednesday with militants at Ladha fort in South Waziristan, a day after clashes there which the army says left 40 militants and five soldiers dead.
Meanwhile, tribesmen in the Mir Ali area of North Waziristan have attacked the main grid supplying electricity to North and South Waziristan, disrupting the power supplies in several areas.
A soldier has been reported killed and two other wounded in North Waziristan when militants fired rockets at a fort.