Police and an Explosive Ordnance Disposal (EOD) responded to the 11.20am blast in front of Ban Koh Ta rubber wood processing factory on the road number 409 in Tambon Thung Pla.
They rushed the injured policemen - Pol Lieutenant Manoon Kaewkabthong, Pol Lieutenant Chatree Kaewkan, Police Senior Sergeant Major Apiwat Boonkaewphetch and Pol Sergeant Major Jatupol Akarawibun - and female bystander Limoh Tohteh to Pattani Hospital.
Among these wounded, Jatupon was the most seriously injured.
Suspected insurgents planted a bomb-laden bicycle at the roadside before detonating it when the police pick-up truck passed, police said.