The suicide attacker drove the car into buildings behind the police station at Domail in Bannu district of Khyber-Pakhtunkhwa province early this morning.
The explosion was heard from several kilometres away.
Two women and a policeman were killed and 27 others, including 10 women and children and nine policemen, were injured, police officials said.
Seven houses were destroyed or damaged by the blast.
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Some of the critically injured were sent to a military hospital.
A bomb disposal squad official said an estimated 500 kg of explosives were used in the attack.
In the lawless Khyber tribal region, independent candidate Shahjee Gul escaped an explosion that occurred near his election office in Jamrud area this morning.
No loss of life was reported in the attack.
Personnel of the Khasadar Force cordoned off the area and launched a search operation.
No group claimed responsibility for both attacks.
Pakistan has witnessed a sharp surge in violence by the Taliban and other militant groups ahead of the May 11 general election.