TORONTO - The governing Liberals were at a loss to explain Wednesday why construction is continuing at a gas plant in Mississauga they pledged to shut down during the Ontario election campaign.

Critics are questioning whether the Liberals will be able to keep their promise when they won't say how they plan to move a facility that's getting closer to completion.

Premier Dalton McGuinty also promised to block construction of homes on the environmentally sensitive Oak Ridges Moraine during the 2003 election, but was forced to concede after he took office that he couldn't stop it.

Asked Wednesday whether his gas plant promise would face a similar fate, McGuinty laughed off the question.

"We're working on it," he said. "It's been a bit more complicated than we originally anticipated, but we will relocate that plant."

The Ontario Power Authority is in discussions with Eastern Power Ltd. to relocate the plant, said Energy Minister Chris Bentley. But he couldn't say when a deal may be reached or how much it may end up costing taxpayers.

He also couldn't say why the government hasn't tried to halt construction of the plant in the meantime.

"I understand the interest in the minute-by-minute or hour-by-hour goings-on," Bentley said.

"I think it's probably not in the interest of either the discussions or of the people of Ontario that I engage in those. ... So I'll let the discussions continue."

Both the Progressive Conservatives and NDP said they're concerned about how much taxpayers will have to shell out for cancelling the gas plant and another one in Oakville -- which are both in Liberal-held ridings.

The province is already facing a $16-billion shortfall this year.

The Liberals will sink the province even further into red ink by dragging out the plant's relocation, said Tory Leader Tim Hudak.

For six years, McGuinty supported the idea of building a gas plant in a residential areas, only to change his mind 12 days before the Oct. 6 vote, he said.

"And here we are, more than a month later, and he says what, 'It's more complicated than I thought?"' Hudak said.

"C'mon, that's old-school politics nobody believes. It looks like he's setting us up for yet another Dalton McGuinty broken promise that's going to hit us in the pocketbook."

The Tory leader also promised to shut down the plant just one day before the election. The New Democrats didn't say during the campaign what they would do with the plant.

Residents have long opposed the Greenfield South plant, which straddles the Toronto-Mississauga border, saying it was too close to homes, schools, a hospital, a hospice and a large mall.

In explaining his party's change of heart during the campaign, McGuinty said the community had changed significantly since the plant was proposed in 2005.

Four local Liberal candidates made the promise to stop construction of the plant in a barely publicized announcement Sept. 24.