The investigation into Christchurch woman Yanfei Bao's disappearance is now a homicide inquiry, Detective Inspector Nicola Reeves says.

Bao, 44, has been missing since last Wednesday.

"Police have today elevated their investigation into missing Christchurch woman Yanfei Bao to a homicide investigation. Our search for Ms Bao is continuing with significant police resources committed to finding her and bringing her back to family.

"We have today informed Ms Bao's loved ones of the development and we know it is the news they did not want to hear. Our thoughts are with them and her family is receiving support from police and Victim Support."

Bao's family continued to ask for privacy, she said.

Further charges for a 52-year-old man charged with kidnapping on Sunday are being considered. Police spoke with the man accused with Bao's kidnapping on Saturday evening but Reeves would not "divulge what those conversations were about", she said.

Search efforts had taken place today in around Halswell River, the Green Park area, Lake Terrace Road and the New Brighton Road and Palmers Road intersection.

Police staff remained at a property on Trevor St and public information was a vital part of this investigation, Reeves said. Police wanted to hear from anyone who saw Bao's car on 19 July.

"Police are interested in the movements of the car between when she was last seen on Trevor Street just before 12.30 in the afternoon and when the vehicle was found on Iroquois place at 10.45pm." The car's registration number is PKT556.

A scene examination of the Trevor Street address started yesterday morning, and there was number of aspects, significant information and concern that had come from that address, Reeves said.

She would not go into what had happened at that address, but it was of significant interest to police and of concern.

Police had received over 170 pieces of information to date, and Reeves wanted to acknowledge the public.

"We're in particular areas because particular information we've received are directing us to those areas, we have a dive squad working and specialist teams working.

"I'm certainly very hopeful that we will find her."

Police were keeping an open mind as to whether more than one person is involved, but not actively seeking anyone else at the moment, she said.

The investigation so far

On Wednesday, police continued searching a stretch of the Halswell River, south of Christchurch. The dive squad were also called in to assist, using inflatable boats.

Yanfei Bao was last seen door-knocking in the suburb of Wigram a week ago.

A large police presence could be seen near Neills Road, which is taped off near the swollen river.

Police earlier said they were keeping an open mind about where Bao is and what might have happened to her, but concede they have "grave concerns" for her safety.

A 52-year-old man appeared in court on Monday charged with kidnapping Bao.

He had been arrested at Christchurch Airport on Saturday.

Main image (RNZ/Nate McKinnon): Detective Inspector Nicola Reeves.