Tobeck said the patient had flu-like symptoms.
An ambulance crew was called to a home in the suburb of Otangarei about 8.15am yesterday where the patient was vomiting.
He was taken to hospital as a "status one" or in a life-threatening condition.
Northland is in the grip of a meningococcal C outbreak.
Eight patients nationwide have died of the disease, including Ben Brown, 18, who died in Whangarei Hospital on August 27, 14-month-old Jacob Whyte who died after being transferred to Starship Hospital, and an 82-year old Whangarei woman who died last week.
Northland Health has started a vaccination programme for people aged between 1 and 20.
Northland District Health Board's general manager of chronic and complex care, Neil Beney, wouldn't release any information on Hemi's condition but said there were no confirmed or suspected cases of the disease in the hospital yesterday.
A resident in Hemi's street said two ambulances were at the house for at least half an hour yesterday morning.
Hemi's pastor James Gamble is a close friend and he was with Hemi, a youth leader at Alive Church, when he went to hospital on Friday as well as for much of the day yesterday.
"They're getting tests done, that's all I can tell you at the moment."
The hospital had said it was unlikely Hemi had meningococcal disease but tests back tomorrow or Tuesday should reveal more.
Meningococcal disease is notoriously difficult to diagnose but swift to kill.
Symptoms may include a high fever, headache, sleepiness, a stiff neck, dislike of bright lights, joint and muscle pains and vomiting or, in infants, refusal of food.
A rash occurs in about two-thirds of people with meningococcal disease.
Northland mother Jody Crossley-Coe told the NZ Herald of how her vigilance saved the life of her 15-year-old son Brett last month.
She was aware of other deaths from the disease and kept a close eye on him when he developed some symptoms.
"They said another hour or two hours of not being diagnosed, he could possibly have had some permanent damage. Twenty-four hours and we would have lost him."