Police are planning to use helicopters on Friday in the search for missing Christchurch woman Yanfei Bao.
The helicopters would predominantly be used in a search of Lake Ellesmere, Detective Inspector Nicola Reeves said.
On Tuesday, police searched farmland near the lake, with officers seen walking through long grass and checking undergrowth.
Then on Wednesday – the day police said Bao's disappearance was being treated as a homicide inquiry – the Police National Dive Squad was involved in a search of the Halswell River, which runs into the lake south of Christchurch.
On Thursday, the search of the river was in a rural area, several kilometres north of the lake.
Dive squad members, helped by Surf Lifesaving personnel, were searching the riverbanks from inflatable rescue boats, Reeves said.
The dive squad was using sonar technology to search beneath the surface of the water to identify anything that may be of interest.
Bao, 44, a real estate agent, was last seen about 10am on July 19 on Trevor St, in the western suburb of Hornby.
A 52-year-old man arrested at Christchurch Airport on Saturday with no bags and a one-way ticket to Shanghai, China, has been charged with kidnapping, and police have said further charges are likely.
On Sunday, police seized a property in Trevor St under search warrant, and have been forensically examining it.
Bao had been due to show the house to a prospective buyer on the day she disappeared.
On Thursday, Reeves said large numbers of police had been working across Christchurch in the search for Bao.
On Friday, the search was expected to involve Police Search and Rescue, LandSAR volunteers, Coastguard, Surf Lifesaving, Police Specialist Search Group, Police Dog Team, Garden City Helicopters and AREC (Amateur Radio Emergency Communications).
Reeves repeated a request for information about Bao's silver Nissan Dualis car on the afternoon or into the night of the day she went missing.
The car, registration PKT556, left Trevor St about 12.30pm.
It was found in Iroquois Place, Wigram, about 10.45pm that day, after Bao failed to pick up her daughter from after school care and was reported missing.
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