TORONTO -- Ontario's opposition parties were outraged Thursday after the government announced dozens more documents had been unearthed on two cancelled gas plants, months after the Liberals repeatedly insisted they had all been released.

"We're sickened by this, that's all I can tell you is my stomach feels sick over this, that this has happened in our province," said Progressive Conservative energy critic Vic Fedeli. "We've said all along there are documents that are being covered up."

It was actually the third batch of gas plant documents and the second time the Liberals have been forced to admit they were wrong when they claimed to have publicly released all the relevant pages ordered by a legislative committee.

"I want to know from this premier why anybody in Ontario should have any trust whatsoever in any Liberal in this province," demanded NDP Leader Andrea Horwath.

"The people of this province deserve the answers to why these documents have been withheld from the view of the members of this legislature, as was their right, for months and months and months."

The government was being sincere when it told the legislature several times last fall that all the relevant documents requested by a legislative committee had been released, said Energy Minister Bob Chiarelli.

"We took the initiative when we found out about these documents to release them of our own volition," said Chiarelli.

"That should be evidence of our willingness to be open and transparent, that when we found out there were more documents they were immediately made public."

The Tories and NDP have said for months they were convinced the Liberals were still hiding documents on the cancellations of the energy projects in Mississauga and Oakville, which cost taxpayers at least $230 million.

They've accused the Liberals of cancelling the plants to save seats in the face of local opposition to the projects.

Premier Kathleen Wynne said she was notified about the newly found documents late Wednesday.

"This is an ongoing process and it's very complicated," Wynne told the legislature.

"It's disappointing that we didn't know about it, but we want all of that information to be out in the public."

The NDP accused the Liberals of deliberately trying to cover up the documents.

"This has been an ongoing process of obfuscation of the facts by this government, that's what the ongoing process has been," said a fired-up Horwath.

There is still no sign of any documents related to the gas plants from the premier's office or the ministry of energy, even though more than 56,000 pages have already been released, said the Conservatives.

"If they're going to give us 600 (new) pages when we have 3,000 that are whited out that I presented in this house, we know they're not telling us the full story again," said Fedeli. "It's absolutely sickening."

Ontario Power Authority CEO Colin Andersen said they told the Energy Ministry last November that they had missed some terms, such as government project code words, and there would "likely" be more documents.

Asked Wednesday whether there were any more documents, Chiarelli said they'd all been released.

The ministry was involved in co-ordinating the large-scale search, Andersen said. But he didn't feel any political pressure to release or not release documents.

The opposition parties joined forces Wednesday to send a contempt of parliament motion over the release of the gas plant documents to the Justice committee.

Last September, the Liberals told the legislature that all the documents had been released with 36,000 pages, only to find another 20,000 pages a month later.

The New Democrats revived their demand for a public inquiry Thursday to examine all aspects of the gas plants scandal, while the Tories demanded Wynne agree to a committee to examine the controversy.

The opposition parties were not impressed that OPA's top executives were told to hold a news conference to answer reporters' questions about the newly found documents, saying the Liberals were throwing bureaucrats under the bus to protect their decision to hide documents.

Andersen and OPA chairman Jim Hinds issued an apology and said it was inadvertent that the 600 new pages -- which included emails, letters and meeting appointments -- were overlooked in the first two searches. They said they're confident that they've covered all their bases this time.

"We are in the business of producing electricity, not producing documents," said Hinds.

"I don't think cover up is the right way to describe it. We messed up some search terms."

Ontario's auditor general is probing the costs of both the Oakville plant, which was cancelled in 2010, and the Mississauga plant, which was cancelled during the last election campaign.

Andersen wouldn't say whether the cost of relocating the two plants could be more than $230 million.