The shooting occurred on the Paseyawor-Saiburi Road in tambon Paseyawor of Saiburi about 7.30am, said Pol Col Panya Karavanant, chief of the Saiburi police station.
Five officers were patrolling along the road in a pickup truck when gunmen in another pickup truck fired at them with assault rifles. The policemen fired back and the attackers sped away.
Pol Sen Sgt Maj Pongsak Srikhirin, 45, and Pol Sen Sgt Maj Niphon Nuangkota, 45, were shot dead on the spot.
Pol Sen Sgt Maj Khamsri Simma, 47, Pol Sen Sgt Maj Savarak Sudsoongnoen, 44, and Pol Sen Sgt Maj Kuang Thaprakone, 46, were seriously wounded and rushed to Saiburi hospital.
Police blamed separatist militants.