Victoria's dirtiest power station, Hazelwood, will be closed within months.

The closure will bring to an end more than five decades of cheap, brown-coal-fired electricity generation at the plant and cost up to 900 Latrobe Valley jobs.

Hazelwood's majority owner, French power giant Engie, is set to announce the plant's closure on Thursday.

As revealed by Fairfax Media, the plant will be completely shut down by April 1 next year.