A group of 16 remaining protesting prisoners continued to light "significant" fires overnight at Waikeria Prison, Corrections say.
The situation has been ongoing since Tuesday afternoon, when inmates lit fires in the prison yard as others went onto the roof in protest.
Fire services, police and St John staff remain at the grounds and are working with Corrections staff.
Incident controller Jeanette Burns said this morning: "We are absolutely committed to ensuring that this incident is resolved safely."
She said there were multiple risks involved - including the structural integrity of fire-damaged buildings, weapons available to the inmates involved, and the toxicity of burnt building materials.
Burns also pinpointed the violence "being offered" by the prisoners.
Specialist Corrections staff are involved in the situation, in a bid to negotiate with those involved still.
Corrections said anyone who surrendered would immediately be given food and water, as well as support.
"As prisoners surrender, they will be secured, searched, provided with food and water, assessed by medical staff and will have access to kaumātua and other support."
Burns said they had a duty of care to the men involved.
"It is likely that they will remain in our custody for a number of years to come."
A police spokeswoman said this morning officers remained on the ground helping staff from Corrections, which is the leading agency for anything to do with the incident.
In the past few days, information has trickled out of the prison about the reasons behind the riot.
Sources have said the men were making a stand against conditions they had experienced at the prison facility over the past year.
"Our water comes out brown," one inmate told Radio NZ.
"But we still have to drink it. We sit and eat in the same room we sleep in.
"We get [a] towel and clothes changes once a week - clothes that don't even fit."
Last night, Corrections said: "They have had multiple regular opportunities to comply with staff."
The damage to the facility has been described as "extensive" and prisoners have forced their way through to restricted parts of the prison.
One of the rooms they have broken into stores tactical equipment including power tools, batons and body armour.