Ardern said "myself and all our Maori MPs feel that weight of expectation" about practical things like jobs, housing and lifting people put of poverty.
Earlier the marae near Kawakawa hosted a powhiri for the PM to mark Davis' appointment as Minister for Crown-Iwi Relations.
Ardern arrived with partner Clarke Gayford, Green Party co-leader James Shaw and a raft of ministers including Andrew Little, Peeni Henare and Davis.
Other Labour MPs with family links to the marae include Peeni Henare, Willow Jean Prime and Nanaia Mahuta.
The marae last hosted a Prime Minister in 2008 on February 5 when Helen Clark went to the Ngati Manu marae at Karetu instead of Te Tii Marae.
That was to officially mark the selection of Davis as a Labour Party candidate.
The opening speaker acknowledged that visit, recalling former MP Dover Samuels had suggested it be a regular event.
He drew laughs when he muddled up the names of Jenny Shipley and Helen Clark.
The powhiri included a range of speakers welcoming Ardern but also telling some tall stories.
One advised Ardern that Karetu was "the centre of the universe and we are all great breeders".
Another speaker's attempt to tell a rather long joke involving former PM David Lange, his minister Koro Wetere and advice to Lange to please his wife by taking his clothes off and doing haka for his wife was derailed.
Those present clearly decided it was heading in an area inappropriate for the PM's ears and simply started singing a waiata, signifying time was up.
Ardern has promised Karetu Marae she will return, saying for her "no Marae is too small".
She read a greeting in te Reo, before joking about the notes she was holding.
"There will be no Marae too small for this Government."
She promised to return "that is if you'll have us".
Ardern also regaled them with anecdotes about the late Parekura Horomia, remembering he had called her "girl" and would be amazed to see where she was now.
She remembered renting a tiny rental car for a long drive and Horomia asked for a lift.
"Every time I changed the gear I had to grab it from within his outer thigh: it was a very intimate experience we had together."
Ardern also joked about her Maori MPs, saying Peeni Henare had "made the ultimate sacrifice by giving up fishing for Parliament".
On a more serious note, she said Henare was one of those she went to for advice and had a "quiet, dignified leadership" about him.
She recalled Rino Tirikatene's digested election slogan "We Need to Just Kick Some Butt".
She saved her warmest praise for Kelvin Davis.
She said Davis was so competitive "I hear you had no qualms in a rugby match once stealing a ball from a one-armed man".
Ardern spoke of the time she had taken on the leadership and had asked Davis if he could take on the deputy role. His response: "I'll do what you need me to do."
She referred to the time Davis walked the length of the North Island to highlight the issue of child abuse and his visit to Australia.
Davis came under fire in some quarters for performance as acting PM when Ardern was out of the country last year.
Ardern warned him to be ready to try out her job again.
"I should warn you I'm going away again in March so you're going to have to be Prime Minister again."
Ardern said that as she had previously discussed with iwi chairs and members of regional and local government, the government had a lot of things it wanted to achieve, which it could not do alone.
"I think we're only going to make the gains we would like to make if we work in partnership."
Ardern said it was not about the government dictating what should happen but rather working together with people in the regions such as Northland to identify the problems.
She listed regional roads and regional employment as examples.
"The provincial growth fund is a key opportunity that we have to say to local government 'what things in your area would unleash jobs', so rather than us dictating, sitting down and funding out what the opportunities are."
Ardern said an "obvious" example of an area that could get funding was forestry in Northland, which creates job opportunities and helps tick off environmental goals.
She said Northland mayors had raised access to the region as key.
While she would not confirm whether or not access, including roads, to Northland would receive funding the government wanted "to make sure that our regional roads aren't neglected anymore"
Ardern said the government wanted to take the Crown-Maori relationship beyond the negotiating table, something Minister for Crown/Māori Relations, Kelvin Davis would help carve out.
Ardern said in Davis' first 100 days as Minister for Crown/Maori Relations, he had achieved some specific housing initiatives, which they weren't ready to discuss yet.
Kelvin Davis has acknowledged the tribute his Marae and the Prime Minister have paid him at his home Marae of Karetu.
The event was supposed to be surprise for Davis - although in the North there is no such thing. Standing to speak, Davis quipped "well this is a surprise," drily adding "as much of a surprise as an open invitation on Facebook can be."
Davis has been appointed to the newly created ministerial role of Crown Iwi Relations, a role to reflect many iwi have now signed their settlements.
Davis said on February 5 it would mark 10 years to the day he was confirmed as a Labour candidate by then PM Helen Clark at the marae.
He recalled asking the kaumatua if they could put on some tea and scones for the Prime Minister. The elder replied it was the first time the marae had hosted a Prime Minister. The resultant hakari (feast) had filed tables in several marquees on the marae grounds.
Davis ended by thanking those who had come but acknowledging it was probably more for "selfies with Jacinda" than for him.
The people of Ngati Manu said it was great for the Northland hapu to have the Prime Minister come to their marae.
Helen Locke, of Ngati Manu descent who also played a part in welcoming Ministers and MPs onto the marae, said it was good to see Prime Minister Jacinda Ardern in Karetu.
"It's great honour for our hapu but it is definitely not to take the light away from Kelvin Davis and our other Ngati Manu MPs."
Meanwhile Sonny Tangira who was at the marae with his moko said it was "beautiful".
Meanwhile thousands of New Zealanders in Australia are celebrating Waitangi Day early, with an event in Sydney.
Labour backbenchers Kiri Allan and Tamati Coffey are heading over to speak. Last year the then Labour leader Andrew Little did the same.
Allan said New Zealanders across the ditch don't get a statutory day but they create their own events to commemorate with music, speeches and Kapa Haka.