A Christchurch toddler who died in hospital late last week was the victim of a sustained and brutal assault, police say.

Fifteen-month-old Ihaka Stokes was taken to hospital on Friday night but died shortly after.

Police are interviewing a number of people but are yet to make an arrest.

Detective Inspector Greg Murton said the assault is the worst he's seen in his police career.

"The scene examination and post-mortem results have confirmed that Ihaka was the victim of an extremely violent assault, or assaults, and has subsequently died of his injuries," Murton said.

Police are interviewing a number of people but are yet to make an arrest.