Last year, according to an issues paper presented to the government in September, claims rose 21 per cent on the previous four years.

The government's insurer, Comcare, says an increasing number of people are being harmed at work, with particular rises in mental health harm; and people harmed at work ''are not recovering as quickly as they should'', with lost work-time rates rising.

It says ''external economic factors such as the mismatch between market inflation expectations and interest rates'' were also to blame.

Earlier this year, Comcare's deputy chief executive officer Steve Kibble wrote to the CSIRO to advise that its premiums would rise from $1.9 million to $4.9 million, reflecting overall rises in government agency premiums.

''The scheme is under pressure,'' Mr Kibble wrote.

''Liabilities have grown significantly and reflect an increasing number of people harmed at work, in particular, the incidence of mental harm claims.''

He said people being harmed at work were not recovering ''as quickly as they should'', people were absent for increasingly long times, and there were ''poor'' return-to-work rates for people with long-term incapacity claims.

To cope with the rise in claims and reduced interest rates, Comcare has this year increased the scheme's premium pool from $239.8 million in 2011-12 to $310.4 million in 2012-13.

This represented a 25.5 per cent increase in the average premium rate, it said.

The agency's chief actuary, Bruce Watson, said ''over time we've seen a change in the mix of claims. They're more complex, particularly when there's mental harm claims.'' These took longer to resolve.

He was unable to speculate on why mental harm and other claims had risen so much.

Workplace Relations Minister Bill Shorten has ordered a review of the Comcare scheme, which is being led by public and administrative law barrister Peter Hanks, QC, and former top-ranking bureaucrat Allan Hawke.

Mr Shorten's spokeswoman said the increase in premiums ''creates the right incentives for employers to help workers rehabilitate faster''.

''Whilst there has been an increase in the number of workers' compensation claims, in particular mental harm claims, the duration of time taken off work by injured workers covered by the Comcare scheme is consistent with the national average,'' she said.

''The aim of the review is to modernise the federal workers' compensation scheme to ensure injured workers are given every opportunity to return to health, independence and work as quickly as possible.

''It is the government's intention that the review will not consider any reduction in existing benefits afforded to workers covered by the Comcare scheme.''