More than two dozen motorcyclists had to be rescued from deep snow as they made their way to a rally in Central Otago over a closed road overnight.

Police were left "shaking their heads in disbelief" after having to rescue the group which ignored road closed signs on the Danseys Pass Road, said Sergeant Ian Kerrisk of Alexandra police.

The group, aged from their early 20s to mid 70s, had intended travelling over the pass to the Brass Monkey Rally at Oturehua. The annual rally attracts hundreds of motorcyclists - drawn to the cold and "one of the last great motorcycling adventures".

However, they got more than they bargained for when they became trapped just below the summit at lunchtime yesterday and spent several hours on foot trying to walk the 14km through snow to the Danseys Coach Inn.

A helicopter could not be put up because of the weather but police and search and rescue staff in 4WDs managed to travel 2km up the road from the hotel and found a group of 20 riders.

A local farmer, on his tractor, and a grader took searchers through the deeper snow further up the pass and they found another three riders 3km up the road. Three more were found sheltering near the roadway further up.

Snow near the summit of the pass was shoulder deep in places, Mr Kerrisk said.

"The riders were all extremely cold and tired and very grateful to see the searchers. They had been trying to walk through snow for some seven hours at that stage in freezing conditions and were nearing the end of their endurance."

The riders were taken back to the hotel to warm up. After a warm drink and a hot meal none needed any further medical attention.

The pass was closed last week but the riders managed to get past the locked gates and at least three warning signs, Mr Kerrisk said.

"Their decision to travel that road past warning signs and locked gates is foolish to say the least and could well have resulted in the loss of life. They not only put themselves at risk but caused others to have to risk the conditions to rescue them."

Police were reviewing the incident but charges were unlikely against any of the riders.

"At the end of the day they made a bad decision and they will have to answer to their families and peers for that. I hope this will be a learning curve for those involved."

He said a donation to the local Maniototo Search and Rescue organisation would be appreciated by the local community, but that was a matter for them.

"We got everyone out safely and for all the people involved in the rescue that is reward enough."

Mr Kerrisk said the riders accepted they had made a bad decision.

However, while the group had put themselves and their rescuers at risk, he had nothing but praise for the Brass Monkey Rally itself.

He said there have so far been no incidents involving the riders over the weekend, despite icy conditions making the roads difficult for the nearly 2000 riders attending the rally this year.

Stan Hansen, chairman of the Otago Motorcycle Club's Brass Monkey organising committee said there had only been one similar incident associated with the rally, and that was more than 20 years ago.

The club did not condone riders travelling on closed roads.

"It's closed for your safety," he said.

Temperatures at the rally dropped to about minus 2degC last night, but were down to minus 6degC on Friday night, he said.