A police spokesman said Christchurch police were back at the scene coordinating a response.
There were no further updates at this stage, he said.
Flynn Parker was at the scene yesterday and said there were around three to four police cars and two ambulances involved in the rescue at the popular rope swing site.
"A helicopter came in very swiftly and was searching for two hours back and forth in the trees. Around four boats, including the harbour master and kayaks, etc, all were looking in the water."
He said kayaks, boats and a bunch of people on little orange boats had been searching for the swimmer near the rope swing.
"Not looking very hopeful, sadly."
The search comes after a child died in a suspected drowning earlier in the day at a Christchurch pool.
A distraught woman was heard yelling "that's my baby" as a child was pulled unresponsive from the water.
A police spokesperson said emergency services were called to Waltham Swimming Pool in Sydenham at 2.45pm after reports a child had been found unresponsive.
"CPR was carried out. However, tragically, the child was unable to be revived. Inquiries into the circumstances are under way."
A traumatised woman who was at the pool with her 8-month-old baby told Stuff she was in the toddler pool when she heard the lifeguard's whistle.
She initially thought someone was breaking the rules.
"But then a lady on the grassy hill ahead of me screamed 'that's my baby' and she and a group of people ran from the grass to the pool, where a child was being pulled out."