Police say its dive squad will on Wednesday search Christchurch's Halswell River in the week-old hunt for missing real estate agent Yanfei Bao.
Officers will also comb the nearby area of Greenpark, about 17km from Wigram where Bao, 44, went missing while doorknocking last Wednesday.
"We are keeping an open mind as to where Yanfei is and what may have happened to her but we do have grave concerns at this time," a statement from Det Insp Nicola Reeves said.
"As such, we are considering all possible lines of enquiry and making every effort to locate her," Reeves said on Wednesday.
On Sunday, a 52-year-old man was arrested and charged with kidnapping Bao - with further charges and arrests not being ruled out.
Officers on Tuesday zeroed in on a property on Christchurch's Trevor St, also not far from where Bao went missing. Police would remain at that address on Wednesday, Reeves said.
"Police would like to acknowledge their appreciation of the public's assistance over the past few days.
"The investigation team has received a number of pieces of information and are working through each report.
"Every piece of information is valuable to understanding what has occurred since Ms Bao disappeared."
The investigation is ongoing and sightings of a silver Mitsubishi sedan with the registration DPH101 are still being sought, Reeves said.
Anyone with information was urged to contact the police on 105, quoting file number 230720/5911.
Timeline
Bao, a mother-of-one, recently joined Harcourts as a real estate agent and has extensive experience in sales.
She was last seen on Vickerys Rd in the middle-class area of Wigram at about 10:30am last Wednesday. Her car was left parked on Iroquois Pl.
Police and Bao's family have said her disappearance is very out of character and there are deep concerns for her safety.
Officers earlier located one of her cell phones nearly 7km from where she was last seen. Investigators found it in the grass berm along the Southern Motorway thanks to assistance from the public.
Investigators have now searched three properties as part of the probe, dubbed 'Operation Helo'.
