The prime minister has released a letter outlining Winston Peters' duties while she is on maternity leave.

Deputy prime minister Mr Peters will act in Jacinda Ardern's role during the six weeks she takes off after childbirth. She is due on 17 June.

In her weekly post-cabinet media conference, Ms Ardern said the working arrangement was exactly the same as when she travelled overseas.

"This is all set out in the cabinet manual," she said.

"The only thing that's different is the length of time."

Despite there being no change to the usual arrangements, the government was publishing the details due to the public interest, Ms Ardern said.

"There has been a lot of questions, so for the sake of clarity, we've been quite happy to put out what is our usual way of functioning in the public domain."

Both leaders had drafted the letter together, Ms Ardern said.

Mr Peters would manage the day-to-day business of government, such as answering questions in parliament and attending official engagements.

He would continue to consult Ms Ardern on major issues and matters of national security.

"I imagine it will be dialogue both ways," Ms Ardern said.

"I may, from time to time, call the Acting Prime Minister and he may choose to call me."

Asked how he was feeling ahead of assuming his new duties, Mr Peters said he was "ready for it".

"I was doing this job 22 years ago."

Before assuming his temporary duties, Mr Peters will travel to China in about a week, the first visit to China from the new coalition government.

The trip has not been formally announced but Mr Peters said today he would be in China for four days.

New Zealand and China are currently reviewing the free trade deal that was signed in 2008.

Mr Peters said the visit was to extend the relationship when trade matters were "seriously critical".

Other issues up for discussion included North Korea, which Mr Peters said it would be good to share perspectives about, and how the two countries could work "profitably and beneficially" in the Pacific.