Police say "uninvited guests" arrived at a 21st birthday party where two men were killed and three critically injured in a mass brawl overnight.
The brawl took place on Lytton Road in the Gisborne suburb of Elgin at 11:30pm on Saturday and involved about 100 people, according to police.
Two men were found dead at the scene and a homicide investigation has been launched.
Police said three others were taken to hospital in a critical condition and a number of police units were needed to gain control of the scene.
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Acting Tairāwhiti Area Commander Inspector Darren Paki said police - including the armed offenders squad - were called to break up an altercation following a 21st birthday party overnight.
Staff attempted to resuscitate two people who were later declared dead, while three others were taken to hospital with injuries.
A 45-year-old man and 21-year-old man are both in a serious but stable condition with suspected stab wounds.
A 30-year-old man is in a critical condition in the intensive care unit.
One person has been arrested and is assisting police with enquiries.
"Our investigators are now piecing together the events leading up to the altercation, but initial indications are that the party was attended by a large number of family members, when two uninvited guests arrived," he said.
"This is very clearly a distressing situation for the community and particularly for the families now grieving loved ones. What should have been a happy occasion for this family, fuelled by alcohol, has turned into an ugly and an awful tragedy for the people involved."
Police remain at the emergency department of Gisborne Hospital, where access to the emergency department is being managed.
"Our staff will be on high alert and monitoring ongoing activity and initial indications are that the conflict did not involve rival gangs," he added.
'It really is heartbreaking'
Gisborne Mayor Rehette Stoltz told Newshub the outcome of the situation was "heartbreaking".
"This is not the news anyone wants to wake up to," she said.
"At this stage we know two people died overnight and that there was a brawl with approximately 100 people involved."
When asked how she feels for those impacted by the event, she said: "It really is heartbreaking to the public of Gisborne and for the whānau involved."
"I want to reassure the community that the police have our back and want to make sure everyone in Gisborne feels safe. It's a tough time for the community."
Stoltz urged those in the area to "be kind to each other and make sure everyone is okay".
"We live in a wonderful community where something very unfortunate has happened. It is a sad day for Gisborne, but we are all working together," she said.
Police Minister Mark Mitchell is on his way down to Gisborne, where the pair will be holding discussions.
"The Police Minister immediately reached out and reassured [us] that we have the full support of police and increased numbers of police on the ground. That includes officers coming in from other towns."
Mitchell told Newshub he spoke with the acting Commissioner this morning.
"I am confident that Police are deploying adequate resourcing to Gisborne to get on top of the situation and provide reassurance to the public."
