A homicide investigation is under way after the death of a Christchurch woman treated in hospital after a serious assault three weeks ago.

Michelle Mary Lawrence, 41, suffered critical injuries after being assaulted at a house on Worcester St in Linwood on June 10 and died in Christchurch Hospital on Saturday night.

An autopsy is expected to be held today.

Timothy Joseph Foley, 52, of Christchurch, appeared in court on June 11 charged with wounding with intent to cause grievous bodily harm.

Police said he was known to Lawrence, and alleged he assaulted her some time before 1am on June 10 at the Worcester St address.

Detective Senior Sergeant Corrie Parnell said the investigation was now being treated as a homicide and further charges were likely.

Lawrence had been in intensive care since her admission to hospital. Her family issued a statement thanking staff at the hospital's intensive care unit for their "wonderful care of Michelle".

"Michelle was a much-loved integral part of our family, a wonderful mother, nana, daughter, granddaughter, sister and aunty who loved life and lived it to the fullest," it said.

"She will be dearly missed by all who loved and knew her."

They asked for privacy in a "very hard time for us".

Police conducted a detailed scene examination for several days after the assault and called for sightings of a green Toyota Camry with the registration number ST 8323.

"We are keen to hear of any sightings of this vehicle during the past 24 hours.

"It may have been in the Sumner and Waimakariri River areas as well as in Christchurch city," Parnell said on June 10.

Police searched the Waimakariri River, in the McLeans Island area, for "items of interest" in the week after the assault.

At the time, Parnell would not say what items police were searching for, but said no items were found.

Police were not planning to search the area again or in other areas. No-one else is sought over the assault.

- © Fairfax NZ News