Torrential rain closed the last 50km link in the highway, between Haast and Paringa, on the evening the road was opened on November 6, 1965.
Anniversary organising committee member, and former Haast Pass Highway engineers representative Les McKenzie told the Otago Daily Times this week that despite the initial closure of the road, the highway provided a crucial link between the top and bottom of the island.
''It really fell out of the sky that night.
''But the highway meant it changed virtually overnight from having no traffic going through Westland to Otago to all of a sudden having quite a lot of traffic,'' he said.
Organising committee chairman Wayne Allanson said the commemorative celebrations from November 6 to 8 would involve people who had helped build the road, local politicians, and the Westland community.
He said despite Prime Minister John Key declining an invitation to attend the anniversary, the weekend would still be an important milestone for the area.
''One hundred and sixty people have registered, but in true West Coast fashion we imagine more people will register closer to the weekend.
''It has been a huge task to bring it together, so it's actually going to be wonderful to see the weekend finally come around,'' he said.
The 50th anniversary will include a get-together tonight at the Haast hotel, a re-enactment of the Knights Point opening, and a dinner tomorrow at which speeches will be made by West Coast MP Damien O'Connor, former road worker Murray Darling, Darrum Habell, and Peter Connors, from the New Zealand Transport Agency.
