A coroner's investigation is underway after the death of an 18-year-old who was re-admitted to hospital a week after an altercation in Hamilton.

The youth died in Waikato Hospital on Friday.

Police spokesman Tony Sasso says the man had been in a fight the previous week.

Mr Sasso says the teenager was back in hospital on Thursday night and died the next day.

A post mortem examination scheduled for today is expected establish the cause of his death.