Simon Tong has resigned as managing director of Fairfax New Zealand to take up an executive role at ASB bank.

He announced his decision to staff six days ahead of an expected ruling by the country's competition watchdog on Fairfax NZ's proposed merger with rival publisher NZME.

The Commerce Commission had not responded by Thursday afternoon to a request for comment on whether the resignation could delay or impact the merger ruling, or whether that was still on schedule.

Fairfax Media's Sydney-based chief executive Greg Hywood said Fairfax New Zealand chief operating officer Andrew Boyle would step in as acting managing director in New Zealand.

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Tong, who joined Fairfax in 2013, will leave Fairfax on Friday week and begins as ASB's executive general manager responsible for technology, innovation and payments on March 27.

The role is part of ASB's leadership team and reports to chief executive Barbara Chapman.

Tong said in a message to staff that it had not been an easy decision. "The speed and level of change the media industry is experiencing is unprecedented and I feel extraordinarily privileged to have been part of that journey.

We're excited to be welcoming Simon Tong to the ASB executive team, as our new Executive GM of Technology, Innovation & Payments. — ASB Bank (@ASBBank) March 8, 2017

"However, in consultation with my family, I came to the decision that it was time to seek out new challenges," he said, adding it had not been a spur of the moment call.

Tong did not make reference to the planned media merger in the statement but said his time at Fairfax had opened his eyes to the importance of "a free and vibrant press".

Hywood said Tong had been an outstanding leader of Fairfax's New Zealand business.

Andrew Matthews, a competition law expert at Matthews Law in Auckland, said this week that the Commerce Commission's ruling on the Fairfax/NZME merger could go either way.

NZME shares have regained all the ground they lost in November after the commission issued a draft decision indicating it would reject the merger. The company's shares were trading at 85 cents on Thursday morning, up nearly a third on their share price in mid-February.

Fairfax NZ's publications include Stuff, The Dominion Post, The Sunday-Star Times and The Press.