The cost of the Victorian Government's 24-hour weekend public transport trial has already blown out by $34 million.

The Government said the so-called Homesafe trial would now cost $86.3 million, not the $50 million Labor budgeted for before the election, because of the cost of extra security.

Under the plan Melbourne's trains will run every hour and trams every 30 minutes on six routes from January 1.

Trains will leave Flinders Street station every 60 minutes on all lines and trams will run on the 19, 67, 75, 86, 96 and 109 routes.

Buses will also leave Southern Cross station at 2:00am bound for Bendigo, Ballarat, Traralgon and Geelong.

Victoria Police will be given extra funding to hire 62 new transit police and 109 protective services officers (PSOs) to keep shift workers and people out at night safe.

The PSOs will only be at the busier "premium" stations, including Flinders Street and Richmond Station.

Public Transport Minister Jacinta Allan said the Government sought advice from police and Public Transport Victoria which resulted in funding extra PSOs and transit police at a cost of $34.1 million, on top of public transport costs of $49.5 million.

"We do recognise obviously that the total figure is above what was initially indicated," she said.

"They're saying to make this work ... we need more drivers, we need more police, we need more PSOs.

"We would really be encouraging the community to use this, to give us their feedback.

"If the Victorian community do want to see this continue, then the best way to demonstrate that is by making the best use of the Homesafe trial."

Opposition spokesman Michael O'Brien said the Coalition had repeatedly warned Labor it had not properly budgeted for the all-night public transport trial.

"A 66 per cent blowout is just huge," he said.

"[Premier] Daniel Andrews hasn't just missed this budget by an inch, he's missed it by a mile."

Mr O'Brien said the absence of PSOs at all stations signalled the undoing of the former government's policy of putting armed guards at every Melbourne station between 6:00pm and the last train.

Public Transport Users Association spokesman Daniel Bowen said the Government would need to examine the frequency of the all-night trains, which run every 20 to 30 minutes in other cities overseas.

"A lot of people will welcome 24-hour weekend public transport. The catch will be those hourly trains — will people be willing to wait up to an hour to catch a train home?" he said.

"Hourly really isn't good enough to encourage a lot of people to use those all-night trains."