Key was commended for his commitment to advancing development in PNG and in the Pacific generally.
"New Zealand is one of our closest partners and a great friend of Papua New Guinea. Engagement between the political leadership of our countries is very important, and I am sure that we will continue the strong relationship I have had with John Key," Prime Minister Peter O'Neill said.
O'Neill said there were many areas in which cooperation would continue to be advanced, including health, education and the small to medium enterprise sector.
"New Zealand is also offering substantial support as Papua New Guinea prepares to host the APEC Summit in 2018. I will be extending an invitation for Prime Minister English to visit Papua New Guinea at his earliest convenience," O'Neill said, adding that it was a testament to Key's character that he has chosen to leave office at a time of his choosing.