UPDATED 5.32PM: One of the Labour Party's longest-serving MPs is stepping back from her electorate seat.

Deputy leader Annette King, a former health minister, won't be standing again in the Rongotai seat in Wellington.

She'll remain on the party list.

When asked if she had been told to step down, Mrs King said "certainly not." 

"It is a decision that I have thought about for some time, talked it over with my husband, and decided it's the right thing to do," she said. 

"No one's ever asked me to step aside - quite the opposite."

Mr Little is confirming Mrs King's decision was entirely a personal choice and wasn't a part of party politics.

"There's not an agreement. She indicated to me a short while ago that is where her thinking and that's what she wanted to do. She's obviously clarified that now with herself and she's made the announcement that she's made."

Mrs King has held the seat for 24 years and her decision to stand down is believed to open a door for the party's leader Andrew Little, who is a list MP and lives in the electorate.

Mr Little is yet to confirm whether he will stand there, saying he is still considering it.

He said being a leader as a list MP means he's not bound to any one part of the country over another.

Mrs King, 69, said she hoped to be health minister in the next Labour government, but it was possible she would leave if Labour was still in opposition.