A Rohingya refugee with serious physical and mental health conditions has died on Manus Island with police believing he took his own life.
Manus Island detainees and advocacy groups say the man fell from a vehicle on Tuesday morning while travelling from refugee accommodation into the island's main town.
He hit the road and died from his injuries at the scene.
Manus province police commander David Yapu said the man's body had been taken to the local hospital and officers were speaking to other refugees who witnessed the incident.
"The motive of his death is not known but it is a suicide case," he said.
Kurdish refugee Behrouz Boochani said the man had suffered through a long history of serious epilepsy.
"They tortured him by ignoring his severe illness and after five years of suffering, he choose to kill himself today," Mr Boochani said via social media.
"I am lost for words ... shame on all those who have abandoned humanity."
Greens senator Nick McKim met the man during visits to Manus Island last year.
"Yet another life destroyed by our government's punitive policies," Senator McKim said in Canberra on Tuesday.
Human rights and advocacy groups have described the apparent suicide as tragic and sickening.
"Rohingya refugees clearly cannot return home, given the current situation in Myanmar," Human Rights Watch Australia Director Elaine Pearson said.
"It's a travesty that Australia has forced them to spend the last five years playing a waiting game on a remote Pacific island while living in an insecure environment with cutbacks to mental health and other services."
The man was also known to the Asylum Seeker Resource Centre.
"This man should never have been there in the first place," the centre said in a statement.
"This is a catastrophic policy failure that has taken yet another life."
The UN's refugee agency said the Australian government must take immediate action to avoid further harm.
"With the passage of too many years and the withdrawal or reduction of essential services, the already critical situation for refugees most in need continues to deteriorate," its representative Nai Jit Lam said.
"Australia's responsibility for those who have sought its protection remains unchanged. Our thoughts and condolences are with the man's family today."
Amnesty International has demanded an independent and thorough investigation into the death along with two other apparent suicides on Manus Island last year.
The Department of Home Affairs issued a statement saying it was aware of the death and inquiries should be referred to PNG authorities.
The Rohingya refugee is the seventh detainee sent to Manus Island by Australia who has died.
Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.