He said the co-ordinated attack had begun soon after midnight with the attackers and security forces trading fierce gunfire before the suicide bomber drove a 14-seater bus into the back of the police station's grounds.
The vehicle exploded as it came under fire, damaging scores of shops, a hotel, a school and many houses.
Most of the 30 people injured were security forces and police, though two by-standers were also hurt, he said.
The police station in Mingora, the main town of the Swat Valley, was also attacked by fighters in July, when two members of the security forces were injured.
The building was destroyed in Thursday's attack, with its heavy concrete floors blown apart and its walls reduced to rumble.
Pakistan's government has tried to enlist fiercely independent ethnic Pashtun tribesmen in the northwest to back its military operations against a-Qaeda and Taliban fighters.
But members of the groups have fought back, killing dozens of security forces and also many tribal elders they accuse of backing the government.
The luxury Marriott hotel in the capital Islamabad was hit by a massive suicide bomb on September 20 when a bomber drove a truck containing 600 kilogrammes of high explosives into its outer gates.
At least 60 people were killed in the blast, which officials suspect was carried out by Osama bin Laden's al-Qaeda network.