Gunmen attacked a complex housing Pakistani security agencies in the southern town of Sukkur late on Wednesday, killing five people and wounding more than 30 others, an official and state TV said.
Four explosions were heard in the area, where "terrorists" seized control of one government building, another building was under fire and the wall of a third had collapsed, Pakistan's PTV reported.
PTV said five people had been killed and 38 injured, and that gunfire was continuing in Sukkur, more than 1,000 kilometres (600 miles) south of the capital Islamabad.
Javed Odho, a senior police officer told AFP, that the attack took place in an area where Pakistan's premier Inter-Services Intelligence (ISI) agency, the police and paramilitary had offices.
"Armed people have attacked. Apparently it is an organised terrorist attack, we have sent heavy contingent of police to the site," he said, speaking by telephone from the town.
There was no immediate claim of responsibility. Pakistan's ISI and government security forces are frequent targets for the country's umbrella Taliban movement waging a domestic insurgency.
But Sukkur has been traditionally immune from such violence, more frequently seen in the northwest on the Afghan border or in Pakistan's cities of Karachi, Lahore, Rawalpindi and Peshawar.