Labor and the crossbench plan to zero in on the awarding of contracts for security services on Manus Island as Senate estimates gets underway today.

Key points: Senators have questioned why the contracts were not awarded to a more established company

Senators have questioned why the contracts were not awarded to a more established company The government must show due diligence was done in the tender process, crossbenchers say

The government must show due diligence was done in the tender process, crossbenchers say Home Affairs Minister Peter Dutton said he had "no sight" of the tender process

It's the final week of estimates hearings before the federal election, and the answers provided will help shape the debate around border protection in the upcoming election campaign.

More than $420 million over nearly two years is going to a relatively unknown company, the Paladin Group, that was registered to a beach shack on Kangaroo Island and a PO box in Singapore.

"I think the very biggest question to be answered is — how on earth did this tiny unknown company with no track record ever get $423 million in contracts from the Australian taxpayer?" Labor Senator Murray Watt said.

"You would normally expect contracts of that value to go to large, well-established companies with a track record and with directors with some reputation."

The contracts were awarded in a "limited" tender process, meaning there may not have been any other applicants.

Officials are allowed to use that sort of process in specific situations, such as when only one company is capable of doing a job, but Senator Watt said it seemed odd.

"We know that in early January this year the company was awarded a $109 million contract extension and that was at a time when one of the company's directors was banned from entry to Papua New Guinea, where the contracts operate," he said.

"And at the same time, or shortly after, one of their other directors was charged with money laundering and fraud offences in Papua New Guinea."

The Paladin contract came to light in a story by the Australian Financial Review last week.

The story also reported the Department of Home Affairs made an advance payment of $10 million to Paladin because the company did not have enough money to begin the contract.

Government must show due diligence, crossbenchers say

Those reports have South Australian crossbench senator Stirling Griff worried.

He wants to see a detailed breakdown of the contract and said the government must show that due diligence was done in the tender process and that the company was providing adequate services.

"If you actually do the calculations, it averages out at $1,600 a day to house each and every refugee, not including food and welfare services, which is more than double what you pay in a five star hotel," he said.

"So it doesn't appear to represent value for money in any respect."

Home Affairs Minister Peter Dutton has said he had "no sight" of the tender process.

But Greens immigration spokesman Nick McKim said that was not good enough.

"Hundreds of millions of dollars have been awarded to a shonky company and Peter Dutton's claiming he knew nothing," Senator McKim said.

"Well if he didn't know, he should have.

"I mean you couldn't make this stuff up and it's exactly why we need a federal ICAC, so matters like these can be properly investigated."

Sorry, this video has expired Attorney-General says asylum seekers will undergo further security checks.

But yesterday, Attorney-General Christian Porter told the ABC's Insiders program this had been subject to a "full independent Commonwealth procurement process" and that such procurement processes were often kept at arm's length from the minister.

He said the sums of money involved needed to be seen in context.

"The reality is that doing these types of things offshore in Papua New Guinea and in Nauru is a very costly exercise," Mr Porter said.

"But in exacting that costly exercise we have managed to stop the inhumane outcome of 1,200 people dying at sea, 50,000 people arriving illegally and at its peak 20,000 people being held in immigration detention in Australia."