The Maori King has been admitted to Waikato Hospital having suffered a heart attack early this morning.
A tribal source said King Tuheitia was rushed to hospital having suffered "quite a big heart attack" earlier today.
The person said it was unclear whether the King was conscious or not and what his current state was.
The Herald understands karakia will be held tonight for the king at Turangawaewae marae.
"We are just crossing our fingers and hoping for the best," the source said.
King Tuheitia's health battles have been well-documented and last year saw him stand down from public speaking duties to focus on recovering from his illness.
His son Whatumoana took the role of Te Whirinaki aa te Kiingi to speak on his behalf at public events .
In his annual speech delivered at last week's Koroneihana celebrations, a visibly frail King Tuheitia revealed he had cancer and diabetes.
In a translation of his speech, which he gave in Maori, King Tuheitia said a false picture of his son Korotangi Paki getting off burglary, drink-driving and theft charges was painted by "sensational and factually wrong media reports".
Another source said the King had been a regular visitor to Waikato Hospital because of his health issues.
"I wouldn't say it's critical but it is serious - he's just had a tough week," the person said.
"It's kind of all added up with the cold and all the stress he's been under...his health isn't good."
The source said King Tuheitia's condition had stabilised. The person said he would be taken to a hospital in Auckland for further treatment and more rest tomorrow.
King Tuheitia had been surrounded by his whanau in hospital throughout the day.