Initially, the 312km trail from Mt Cook to Oamaru received $2.75 million funding from the New Zealand cycle trail fund in 2010, but that has already been spent, along with more than another $1.25 million in grants, donations and in-kind work.
At the time, the trail's promoters knew the funding would not be sufficient to take all the trail offroad.
While no more funding is available from the cycle trail fund, Alps to Ocean (A2O) supporters, along with the Waitaki and Mackenzie District Councils, hope an application will be successful and Mr Key will find money from other sources.
The funding is needed for safety reasons and to provide maximum ''rider experience'', the Waitaki council's community services group's manager, Thunes Cloete, said.
''We always knew the initial funding would not be enough to take the whole trail off-road, but there are areas that it is critical for safety reasons,'' he said.
They included the stretch from the Waitaki Dam to Kurow and other sections from Duntroon to Weston.
At this stage, it was not known what distance of road was involved, nor the cost.
Work was being done to determine what extra funding would be needed and it was hoped to file an application before the end of this month.
When a ceremony was held last week to announce the A2O trail was fully signposted and rideable, Mrs Dean, Green Party MP Kevin Hague and Waitaki Mayor Gary Kircher all supported applying for extra funding, Dr Cloete said.
NZ Cycle Trails also supported that for safety reasons.
Mr Key, the instigator of the nationwide project of cycleways, launched the A2O project in 2010 when he was in Oamaru for a National Party conference, by officially opening the last stretch around Oamaru Harbour to the Oamaru Penguin Colony.
Much of the trail is off-road. One the latest sections opened is from the Chain Hills, just east of Omarama, around the shores of Lake Benmore to Sailor's Cutting.
A Friends of A2O group has also been raising funds for the cycleway.
