Prime Minister John Key has joined Australia in condemning South Korea's plan to resume whaling, describing it as a terrible step in the wrong direction.

The plan revealed at International Whaling Commission talks in Panama has raised the ire of animal welfare groups and prompted diplomatic response from Australia and New Zealand.

"It's a terrible step in the wrong direction. We think it's unnecessary, we think it's inappropriate and we don't think the stocks would support that," Mr Key told reporters in Sydney where he attended a business lunch.

"Most people around the world would be disappointed if the Koreans took this step."

Mr Key said the move had taken him by surprise and he had no official warning.

"The government will be putting the issue up during talks with Korean officials," he said.

"Our ambassador in Korea will be taking our position up with foreign officials there, and our foreign minister Murray McCully will be talking to the Korean foreign minister when he sees him next week."

Earlier, Australian Prime Minister Julia Gillard said Australia's top diplomat in Seoul would tell the South Korean government that Australia opposed its plan.