Melbourne Airport has been given long-awaited approval to build a $3 billion third runway, a move it says will boost the Victorian economy by $6 billion a year while also bringing down airfares.

Transport Minister Catherine King granted the approvals on Thursday night, paving the way for the 3000-metre-long runway to enter operations in 2031. But the issue of aircraft noise looms large, with the Greens seizing on discontent in an attempt to capture more seats at the next federal election, due by May.