"That's not an issue the [marae] trustees have raised with us, but we just know the logistics of being there."
Mr Key said he was not concerned for his own safety, but sheer numbers of protesters meant getting onto the marae grounds may become impossible.
Police may not let him go on to the marae if the situation was too volatile, and Mr Key said he had concerns about the safety of his staff.
"But also there is a limit to the practical capacity for the police to deal with the situation safely. I can't put a whole lot of people in the situation where they could be endangered.
"If there are really large numbers of people, that could be overwhelming for the Maori wardens and others to deal with up there."
The Prime Minister said he would do everything he could to attend, and would talk about issues including the Trans-Pacific Partnership (TPP) agreement, the review of Child, Youth and Family and broader economic and education issues.
Ngapuhi co-chairman Rudy Taylor said he would be talking to marae trustees about increasing security on Friday and Saturday if necessary.
"[John Key] will be kept safe. We have had these issues before, if you look at the [old] days they were doing the whole running and the bashing so these fellas are nowhere near them," he said.
"I will talk to the wardens, then I will talk to the trustees on the security. If we find that tomorrow we need to beef it up, I will be telling them we need to [do that]. I think it is going to be handled right."
Mr Taylor was unsure whether increasing security would, however, be a necessary measure.
Ngapuhi elder Kingi Taurua said he was angered that a vote taken at yesterday's hui, which showed most were opposed to Mr Key's attendance, had been ignored.
"It is only a minority, and I believe strongly that those who were against the decision are members of a political party ... there are some here who have been with the National Party for years and years and years, and some of them are my own relations.
"They are National Party members and they have moved against the decision of the tribe."
On reports that this year's commemorations -- in the same week as the TPP official signing in Auckland -- could see the largest gathering of protesters yet, Mr Taurua said he did not know about numbers, but there would be protests.
"There will be people who will try to stop him coming on to the marae ... those in Auckland will be coming here after their [TPP] protest tomorrow, and there are some already gathered here at this moment."
Te Kotahitanga co-chairman Rudy Taylor said it was good news that Mr Key be welcomed.
"The commemorations were built around two cultures, and to recognise the two cultures, and knowing 176 years of Waitangi Day is to give that understanding and feeling between the two."
On possible protests, Mr Taylor said there was significant anger among Maori at a lack of consultation over the trade agreement. But he was not convinced the TPP would make this year's commemorations any more charged than in past years.
Mr Key's attendance was uncertain after conflicting responses from a hui of marae organisers and Ngapuhi leaders yesterday.
He had said if he was not asked to the marae or told he could not speak, he would not go to Waitangi, despite other commitments such as the dawn service, meetings with iwi leaders and his annual Waitangi breakfast.
