The men were shot dead after a mass breakout by inmates from the Buimo jail in the Pacific nation's second largest city of Lae on Friday, police said.
At least 57 remain on the run. Many were serving time for armed robbery, car thefts, and breaking and entering.
Police shot dead 12 prisoners during a jailbreak at the same prison last year. The National newspaper said only 15 of the 87 who fled at the time were caught and most were badly injured.
Amnesty International's Southeast Asia and Pacific director Champa Patel said: "It is alarming that the security forces' first response was to use lethal force against unarmed people without any concern for their right to life."
"The Papua New Guinea authorities must immediately order an independent and effective investigation into these killings," she said.
"They must suspend any officers involved until the investigation is concluded, and hold suspected perpetrators to account through fair trials without recourse to the death penalty."
Crime and lawlessness is rampant in PNG, a sprawling nation where many still live traditional and subsistence lives in remote areas.
Jails in the country -- which is due to host an APEC leaders' summit next year -- are often overcrowded, with prisoners forced to endure poor sanitary conditions, which Patel said was part of the problem.
"Prison reforms and accountability mechanisms are crucial to stop these incidents from happening again. Whatever the crime committed by inmates, they have the right to be treated humanely," she said.
Police have urged those on the run to surrender.
"These are undesirable people and will be a threat to the community," Lae police official, Anthony Wagambie Jr. said.
"I am warning them that they will be caught. They must do what is good for them and surrender."
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