The police officers were shot while on patrol near First Community Bank Limited at about 9 pm, Garissa Police Chief George Losku said.
Losku said the gunmen also stole a rifle belonging to one of the officers. No one has claimed responsibility for the attack and no arrests have yet been made, he said.
The name of the deceased police officer has not yet been released to the public.
Constable Eric Mutuku, who was admitted at Garissa Provincial General Hospital, told Sabahi that he and his colleague had stopped to get a cup of tea when four young men approached them.
"One of the gunmen shot me twice on the shoulder and then proceeded to shoot my colleague twice in the head," he told Sabahi. "The attackers included young boys who I think were between 10 and 15 years of age."
Bessy Muthoni, the owner of the tea kiosk, told Sabahi that she had just served the officers outside the café and was busy arranging soft drinks in a refrigerator when she heard gunshots.
"One of the gunmen ordered me to lie down as they fled in a waiting vehicle," she said.
On September 30th, two police officers were killed in Garissa while on patrol in the Ngamia Road area.