MORE than 20 old Victorian train carriages will be removed from service after a safety audit found they had critical cracks.

Public Transport Victoria and V/Line, Victoria's regional train service, says 22 of the system's older carriages have been withdrawn from service for testing and repairs today.

The withdrawal comes after a safety audit found fatigue cracks in some critical areas of undercarriages.

PTV chief executive Ian Dobbs said V/Line had advised it would remove the carriages after safety inspections raised concerns on their condition.

"We support V/Line's decision to withdraw the carriages for testing and, where necessary, to address any critical issues with the (undercarriages)," he said in a statement.

It may take months before carriages are returned to service after thorough testing, Mr Dobbs said.

Mr Dobbs said the withdrawal would affect 10 per cent of seats and PTV and V/Line were working to organise replacement coaches to minimise disruption.

Shepparton, Warrnambool, Swan Hill, Bairnsdale, and a small number of Geelong and Traralgon trains will have fewer seats.

In November last year, the state government announced 40 extra carriages will be added to V/Line's network by 2016 at a cost of $207 million, with the first to arrive in 2014.