An alleged incident involving a boy being "led" into the Manus Island refugee compound was not referred to Papua New Guinea police until four days after Immigration Minister Peter Dutton sensationally raised it in a television interview.

But the head of the Australian Border Force strongly backed Mr Dutton's view that the incident "contributed" - and, in fact, was "correlated" - to the Good Friday rampage five days later in which drunken PNG soldiers opened fire on the compound.

Border Force commissioner Roman Quaedvlieg said it was "almost inconceivable" that the April 9 event, in which a group of asylum seekers "imported" a boy under 10 into the compound, did not inflame tensions between detainees and the Manus community.

Such tensions had been escalating for 12 months, he told a Senate estimates hearing on Monday. PNG locals were increasingly concerned about refugees' "encroachment" on PNG defence force facilities, as well as lewd, sexualised and "generally disrespectful" comments towards women, and "bartering and exchanging local goods for sex", he said.

In Mr Quaedvlieg's view, the incident involving the boy not only contributed to unease, but "was correlated to the Good [Friday] event". But he revealed it was not referred to PNG police until April 24, 15 days after it happened and four days after Mr Dutton implied it had sparked the Good Friday shooting.

However, Mr Quaedvlieg said "the referral process was under way" from the day of the incident, when the boy's mother was asked if she wanted it brought to police attention. "She said yes and it was," he told the hearing.

Secrecy has shrouded the April 14 rampage and its roots, but new details emerged on Monday, including an acknowledgment from assistant commissioner Kingsley Woodford-Smith that nine people were injured, comprising five contractors, two detainees, a PNG soldier and an immigration officer.

Despite that, Mr Quaedvlieg said he had not requested a report from his own Border Force personnel stationed at the centre, because the incident was still under investigation by PNG. Greens immigration spokesman Nick McKim said that explanation beggared belief.

"When Australian citizens come under fire, including Australian government employees, the Australian people are entitled to know the facts," Senator McKim told Fairfax Media.

"Both the department and the minister have consistently provided false information about this shooting, and when they're called on it they simply refuse to give accurate information."

Meanwhile, the Department of Immigration and Border Protection confirmed Australian-funded operations on Manus Island would continue once the regional processing centre closed in October.

Deputy commissioner Mandy Newton said the capacity of the East Lorengau Refugee Transit Centre would expand to 440 from 298 "at the completion of some additional works being undertaken". Close to 60 men currently live at the centre.

It is envisaged any refugees not accepted by the US under a deal struck with the Obama administration could be sent to the transit centre, or other accommodation, after the main facility is closed.

But immigration officials said any movements "will be a matter of what the PNG authorities do", because Australia will pull out of the island entirely on October 31.

"After the first of November, we won't be providing funded ongoing contracted services at all," department secretary Mike Pezzullo told the hearing. The PNG government might provide some services but "it won't involve us", he said.

Liberal senator Ian Macdonald took issue with the depiction of Australia's nearest neighbour as an unsafe country for refugees, labelling the depiction "racist in the extreme" and claiming he always felt safe in PNG.

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