"We stayed until 11.15pm. We had a few Maotais," he said in reference to the hard liquor which is China's national drink.
He said Mr Xi had wanted a private dinner - it was his wife's birthday - and wanted to reciprocate for Mr Key the next time he was in Beijing.
His parting comment to Mrs Key had been: "Bring your family with you next time."
Both couples have 22-year-old daughters. The Keys' daughter, Stephanie, is studying art in Paris. Xi Mingze is studying psychology in the United States.
Conversations with Mr Xi were held through an interpreter. Mr Key said Madam Peng used an interpreter sometimes but had a very good command of English.
Because it was Madam Peng's birthday (she turned 52), Thursday's private dinner began with "longevity noodles," traditional birthday fare.
"You can't bite them. That's really bad luck. You have to eat them as long as you can because the longer you can, the longer your life."
Mr Xi laughed at Mr Key's attempts to suck up the noodles. "He's got a really, really, good sense of humour."
The dinner conversation traversed diverse subjects such as the Trans-Pacific Partnership, Rewi Alley, cooking skills, and Mr Xi's preference for three-star hotels in China.
Mr Key, who is the chief cook in the Key household, said Mr Xi said he used to be quite a good cook himself but doesn't cook any more.
They got to talking about Mr Xi's accommodation after Mr Key asked him if it was true he stayed in a tent when he recently went to visit homeless earthquake victims - it was true.
"He said 'every town I go to now, I stay in a middle to slightly better than average hotel and I tell them to serve me the local dishes' because he said he liked them but not the really expensive dishes. He said 'if it's good enough for me, it's good enough for the rest of the officials.'"
It was part of his effort to cut down on corruption by officials.
The two leaders also talked about Rewi Alley, a New Zealander who is a household name in China, and who was a friend of Mr Xi's father, a revolutionary hero of the Long March.
Mr Key said the visit had strengthened the political and personal relationship. "The personal chemistry is good. I don't want to overstate these things but they think we are a really good counter-party to deal with."
Before the airport farewell, Mr Xi met new Opposition Leader Andrew Little with Labour foreign affairs spokesman David Shearer, former Trade Minister Phil Goff and former Labour MP Raymond Huo.
Mr Xi said Labour had been a "trail blazer" in developing links between New Zealand and China, including diplomatic recognition in 1972 and the free trade deal signed in 2008.
The visitors attended a showcase lunch at Sky City in which NZ ingredients were cooked in Chinese style.
They were entertained by a performance of popera sensations Sol3 Mio and a parade of four World of Wearable Art entrants.
PM flags support for China's Asia bank
New Zealand is likely to sign up to the Asian Infrastructure Investment Bank, Prime Minister John Key has revealed.
He was talking to the Weekend Herald yesterday about why he thought the visit of China's President, Xi Jinping, had been successful and he believed one of the reasons was New Zealand's independence.
"I was talking to him about this AIIB investment bank,"Mr Key said. "I said it is highly likely we are going to get involved."
President Xi had been talking about the reasons other countries had given for their decisions.
"And he said 'one of the things I like about New Zealand is we just have our own independent voice, that we just make our own decisions'."
The proposal has been led by China but opposed by the United States, Japan, South Korea and Australia.
It has been criticised as being too heavily dominated by China, which would own half the bank, and as a way to assert its leadership in the region over the US.
New Zealand is considering it only now because earlier meetings in China clashed with the election.
China has the sign-up of 21 Asian countries for the bank, which would have initial start-up capital of US$50 billion and would fund infrastructure projects in the region.
New Zealand would be required to front up with about $120 million in start-up capital and have perhaps $600 million in uncalled capital, depending on the final make-up of the bank.
