Earlier, an internal police report said one of the dead men had a suspected bomb strapped to his body.
In addition to the two injured cops, one police officer killed after getting hit by suspected terrorists' auto, one journalist injured, four perpetrators killed while at least one is on the run.
The men had driven their auto into the police yard before getting out to stage the attack, Setyo Wasisto, national police spokesman, told a briefing.
We'll bring more updates for you from the Riau Provincial Police HQ attack as the story develops.
But the attack comes after a series of suicide bombings by Islamist militants targeting churches and a police building in Indonesia's second-biggest of city of Surabaya over the past few days. No group has yet taken responsibility for the attack.
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Local journalist Doddy Vladimir, who was at scene of the attack, said he saw a white Toyota Avanza van hit the headquarter's fence at around 9am (02:00 GMT).
The attack follows a prison riot in Jakarta, suicide bombings in three churches in Surabaya city, the provincial capital of East Java.
All six bombers were killed, including the mother who was Indonesia's first known female suicide bomber. In the ensuing chaos, at least two suspected terrorists, both wearing balaclavas, were spotted getting out of the auto wielding sharp weapons and attacking police officers.
The families have been linked to the local chapter of Indonesian extremist network Jamaah Ansharut Daulah (JAD), which police said was behind the attacks.
The radical group supports Islamic State, whose ambitions have been curbed after losing most of the land it once occupied in Iraq and Syria.