Ontario's governing Liberals are promising to expand a large stretch of protected land around the Toronto region if re-elected next month, a pledge that comes after the province's Tories backtracked on a promise to allow housing development in the green space.

The future of the Greenbelt -- the world's largest permanently protected green space -- has been a political hot potato roughly a week before Ontario's election campaign gets underway.

Premier Kathleen Wynne vowed Wednesday to extend the Greenbelt into ecologically sensitive areas such as the Waterloo and Paris/Galt Moraine complex and the Nottawasaga River corridor, saying the regions have already been put to community consultation.

The exact size of the addition has not yet been determined and the Liberals said that if re-elected on June 7, they will work with municipalities to decide on the final boundaries, which they hope to do by the fall.

Wynne's announcement came a day after Progressive Conservative Leader Doug Ford reversed an election promise to allow housing construction in the Greenbelt, a plan that first came to light in an online video unearthed by the Liberals.

In the video, which was apparently taken during the Tory leadership race earlier this year, Ford is heard promising to open up a "big chunk" of the protected region for development.

After defending his proposal Monday and vowing to replace every piece developed with land of an equivalent size, Ford said a day later that he changed course after consulting with Ontario residents and would listen to those who want the area preserved.

Tory legislator Vic Fedeli said Wednesday he is "thrilled" by Ford's handling of the issue, deflecting questions about Ford's about-face and whether the party's leader was making backroom deals.

"I think the fact that Doug Ford has said we're not touching the Greenbelt, I think that's where we need to be," he said.

Asked about the Liberals' proposal, Fedeli questioned the timing of the announcement and declined to say whether the Tories would support expanding the Greenbelt.

The Greens also voiced suspicions that the announcement was politically motivated.

"If protecting prime farmland, sensitive wetlands and wildlife habitat was truly a priority, then Kathleen Wynne would not be announcing this on the heels of Doug Ford's leaked video," party leader Mike Schreiner said in a statement.

Wynne, who said Ford's dealings with developers "raises serious red flags," stressed that the project had been in the works for some time.

"The announcement, me standing here today, our presence here today, is about a reaction to something that happened that Doug Ford did, but our plan to enlarge the Greenbelt and our commitment to the Greenbelt is not new," she said. "The next steps of that were going to be in our platform all along."

The Greenbelt is a 7,200-square-kilometre area that borders the Greater Golden Horseshoe region around Lake Ontario. It was protected from urban development by legislation in 2005.