A mentally ill female Iranian refugee at Nauru locked herself in her family's unit and set it alight, her husband says, in an apparent suicide attempt that underscores the ongoing mental harm caused by the Turnbull government's offshore processing regime.

The incident follows two self-immolations by refugees at Nauru in the past month - one of them fatal - and a young Bangladeshi man who died of suspected heart failure on the island after an alleged deliberate medication overdose.

Opposition Leader Bill Shorten on Wednesday said deterring people smuggling should not involve indefinite detention in offshore camps, as former Liberal prime minister John Howard sought to cast doubt on Labor's commitment to border protection.

Photos and video of the latest alleged suicide attempt show thick black smoke pouring from the dwelling, which is engulfed by flames. The building was left charred and extensively damaged.

The Department of Immigration confirmed that a fire broke out at the Anuijo settlement at Nauru this week. It refused to comment on whether it was a suicide attempt, saying the incident was "a matter for the government of Nauru". The Nauruan government did not respond to a request for comment.

Refugee Action Coalition spokesman Ian Rintoul, who has been in contact with the woman's husband, said the woman "had long term depression and had tried to kill herself at other times".

Recounting the statement of the husband, Mr Rintoul said the woman, who has a young son, recently told health workers she wanted to kill herself "but no-one paid any attention".

She allegedly "locked herself inside the room and tried to commit suicide", Mr Rintoul said.

He said the woman was rescued by a security officer before firefighters arrived. She was taken to hospital but later released.

"Yet another serious attempted suicide ... it shows there is a worsening situation at Nauru," Mr Rintoul said.

"People are very worried about the situation, they are very worried for themselves. The situation has grown very intense because people don't know what's going to happen and nothing seems to be happening."

Border protection has emerged as a defining issue of the federal election campaign, amid debate over the size and cost of Australia's humanitarian intake and the best way to deter unauthorised boat arrivals.

Labor supports the offshore detention regime, but wants to gradually increase Australia's humanitarian intake to 27,000 a year, and introduce better conditions and independent oversight to detention camps at Nauru and Manus Island.

Mr Shorten on Wednesday emphasised the common ground between both major parties on the issue, saying said neither Labor nor the Liberals were soft on people smuggling.

But he said the tough approach should not require "indefinite detention in Manus and Nauru".

"[If elected] we would engage in regional resettlement with the sort of vigour we haven't seen in the government," Mr Shorten said, adding that he would dispatch a Labor immigration minister "on a plane to talk to the UN High Commissioner for Refugees".

"We will negotiate in a fair dinkum manner to make sure we have regional resettlement but never again will we allow the people smugglers back," he said.

The government routinely points to internal division within Labor over asylum seeker policy, and says the party would unravel the government's harsh measures if elected.

On Wednesday former prime minister John Howard said the Labor Rudd government allowed "50,000 illegal immigrants later and hundreds of drownings", and left border protection "in tatters".

"It took the strength of Scott Morrison and Tony Abbott to restore the situation and we must not risk that happening again," Mr Howard said.

Lifeline 13 11 14 www.lifeline.org.au

Suicide Call Back Service 1300 659 467www.suicidecallbackservice.org.au

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