Scott Morrison says "people smugglers know they won't get through me and Peter Dutton" but would "have a crack" if Bill Shorten became prime minister.
It's the latest message from the prime minister, who is trying to highlight differences between the Coalition and Labor on border security amid fears of an increase in boats.
Mr Morrison said the government had "increased the strength, resource and capability again of Operation Sovereign Borders" after the medevac legislation passed parliament this week against his wishes.
The prime minister said he had been "forced" to act on Home Affairs advice to reopen the detention facility at Christmas Island to "deal with that decision" on the medevac bill.
"Now, I can't describe to you the fury that is within me that I have to now go spend money on opening a centre that I didn't need to open a week ago," he told reporters in Somerset, Tasmania on Saturday.
Advice released by the government said the cost of reopening Christmas Island would be more than $1 billion over several years.
Mr Morrison made reference to a report in the Sydney Morning Herald about people smugglers sending a surge of boats to test Labor's resolve.
He said the people smugglers "are preparing to do that as we speak".
"That's not me saying it. That's them saying it. That's people smugglers going back up the chain to Pakistan. We have other people who are ready to put boats again out of Indonesia talking openly about it."
Mr Shorten brushed off the prime minister's attack, telling reporters: "Under a Labor government we'll have a ring of steel around this country."
"We will make sure that our ADF, our air assets, sea assets, our Australian Border Force have whatever resources they need to defeat people smugglers," he said in Melbourne.
The opposition leader said "it is possible in this country to have strong borders and the humane treatment of people within our care".
Mr Shorten said the government was so worried about boats, but "in the last four years alone 64,000 people have arrived by air claiming asylum and many of those claims are found to be unmeritorious".
"What's happened is this government has stopped the boats and now they're catching the plane," he said.
The Home Affairs Department website shows 27,931 protection visa applications were made last financial year by plane arrivals.
Australian Associated Press