Low cloud and heavy rain in the Nelson region forced the abandonment of yesterday's planned aerial search for missing tramper Alistair Levy, who has not been heard of for a week since reaching the summit of Mt Owen in a southern section of the Kahurangi National Park.

The Nelson Marlborough Rescue Helicopter was on standby yesterday to search an area of interest to the search and rescue team, but the weather closed in.

Pilot Jarrod Colbourne said farmers and locals in the Mt Owen area continued to keep a watch on the weather, and despite a probably clear patch expected on Sunday night, it was not looking good for a while.

Search co-ordinator Sergeant Mike Fitzsimons said poor weather was forecast for the near future. He said while the ground search for Mr Levy had now been completed, it was too soon to say if the official search would be called off.

"My response is we never completely call off a search until it is resolved, and this matter is not resolved, but we don't have people actively in the field," Mr Fitzsimons said.

He said they still planned to complete the aerial check, and would respond to any other information that came forward, depending on what that might be.

Members of Mr Levy's family arrived in Nelson on Friday and were taken through the search procedure. They understand how it developed and what was involved, Mr Fitzsimons said. 

The family expressed their thanks to the police and search volunteers for their efforts. 

Police have held grave concerns for Mr Levy's welfare given how long he had been missing and the rough terrain in the park. 

The experienced tramper was last heard from when he sent a text from the summit of Mt Owen last Sunday. 

The 54-year-old Palmerston North high school science and chemistry teacher had planned to join wife Tracy and other family members in Christchurch on Monday for Christmas. 

Police believe Mr Levy walked over the top of the mountain and had planned to come back via the cafe at Kohatu, where his bike was located this week. He had arranged to leave it there with the cafe owners. 

Brother Graham Levy said during the week that his brother had been tramping for 30 years, but it was not unusual for him not to take an emergency beacon. 

He had been progressively tramping through the entire South Island, from north to south, and the Mt Owen trip was to fill in a gap in that process. 

Nelson Speleological Group president Andrew Smith said people travelling on the south side of Mt Owen ''absolutely'' needed their wits about them.  

''It's not too bad a country to find your way through if you know where you're going, but if you don't, it's tough.'' 

Anyone with information about Mr Levy is asked to phone the Nelson police, 03 546 3840

- © Fairfax NZ News