Some Ontario viewers who tuned in to Hamilton's CHCH television station Wednesday afternoon say they saw a few moments from a graphic adult sex scene.

CHCH and its parent company, Toronto-based media group Channel Zero, have investigated and say the issue wasn't on their end. Instead, they say it's a problem with a cable provider. On Wednesday a representative indicated the problem was with Rogers, but on Thursday said that they can't be sure of that and are investigating a number of providers.

Rogers hasn't responded to requests for comment.

Fanshawe College student Gabe Burchert saw the sex in question around 2:30 p.m. ET at the school's London newsroom.

"I looked up and there it is," he said from the school in London, Ont. The regularly scheduled program was News Now PM.

None of the other televisions in the newsroom set to other stations changed, he added.

The sex scene lasted for about five seconds before it switched back, he said.

"I have to admit it was pretty funny."

Some of our viewers are saying we aired porn a few minutes ago. We did not. Apparently this was an issue with some carriers. —@CHCHNews

CHCH tweeted an apology to its viewers Wednesday evening.

"We have learned that a decoder was reset at one of the cable companies and the first channel it picked up was an adult channel," the statement reads. "We assure you this was an isolated incident which affected a small group of viewers, and did not occur at CHCH Master Control."

"We apologize for the inappropriate content, and will continue to work with our cable partners to ensure this does not happen again."

Rhonda Messieh, marketing manager for Channel Zero, told CBC News that an investigation is ongoing. "Our VP of operations is all over it."

She said as she understands it, the sex was only seen by standard-definition customers.

This is not the first time CHCH viewers have unexpectedly seen graphic sex.

The broadcaster issued an apology back in 2012 after its morning News Now show briefly switched to a sex scene.

The station blamed the mix-up on a switching error at one of the cable companies that carries its signal.

CHCH's website says it is available in over 92 per cent of Ontario households and is viewed by millions nationally each week.

adam.carter@cbc.ca