Premier Daniel Andrews made the announcement in Ballarat and said 30 new X-Trapolis train carriages had been purchased and would be shipped to the Ballarat site in the coming months.

The premier said the carriages would cost between $75 and $90 million, with the 30 new carriages making up five, six-car Metro trains. 

Alstom staff welcomed having the money locked into the May budget after a tense few months in which they thought the current order for eight new trains by July would be the last. 

"This investment is good for workers, good for Ballarat and good for every single person who uses Melbourne's train network," Mr Andrews said. 

"We were elected to invest in public transport, rebuild our economy and get Victoria back to work and we're getting on with it."

The premier said the new order would ensure Alstom's manufacturing future was safe for at least two years.

"In terms of being ready for the network, construction will run throughout this year into next year and by the middle of 2017 all of those carriages, those train sets will be on the metropolitan train network," he said.

"We made the commitment for 30 train sets and 20 velocity carriages. These five, six car sets are part of that thirty. But again, we're going to have more to say beyond today's order and perhaps beyond our election commitment."

Alstom site production manager Michael Selby welcomed the announcement and said his staff could now breathe a sigh of relief. 

"Until now we didn't know what would happen after July," he said. 

Mr Andrews reminded staff that their future was now safer in Ballarat.

"We can never again have a situation where the workers and their families really don't know what their future holds," he said.

"These jobs are secure, these jobs are worth fighting for and Alstom and other rolling-stock manufacturers have a place in our state."