Wind threatened to spoil the three-day party early on Saturday by blowing over the marquee, but it was soon secured.
The weather improved for the rest of the weekend, replicating the fine conditions of 50 years ago when the road was officially opened by Minister of Works Hugh Watt and Nola Cron, of Haast.
The locals could not have wished for better weather and things literally went off like a bomb.
No-one would admit to the explosion at just after 11am on Saturday, moments after Betty Eggeling, of Haast, and Sonny Yates, of Kaiapoi, had cut the ribbon.
Dirt flew high into the air and many in the crowd screamed loudly then laughed.
Mrs Eggeling, who had been among other things a truck driver, and Mr Yates, a roadworks crew member, were pioneers of the Haast Pass, taking vehicles through before the road was opened.
They nearly leapt out of their skins and then laughed with everyone else.
The explosion occurred out of view of the crowd, behind J. J. Nolan's truck, which had been set up as a stage for the speeches.
Event committee member John Cowan denied all knowledge.
"Honestly, I am on the committee but I don't know who did that. Someone had some high-jinks, though," Mr Cowan said, laughing.
Earlier, an unexpected flyover by a DH89 Dominie, owned by the Croydon Aircraft Trust at Mandeville, brought tears of joy to the eyes of celebrations' organiser Neroli Nolan.
Before the road opening, the isolated South Westland community had relied on aircraft such as the Dominie and others to bring supplies, transport the doctor, dentist and post, take children to boarding school, or deliver pregnant women to hospital.
The Dominie was in hot demand for scenic flights all day Saturday.
From start to finish, events rolled out smoothly.
On Friday night, 270 people attended the launch of Dave Grantham's book A Road Through the Pass: Roadmaking Haast to Makarora, and a DVD by Tas Smith of Contract Cultivation.
Another 270 attended the official speeches and dinner on Saturday night.
Earlier, Westland Mayor Maureen Pugh opened the celebrations by reading a speech from a lectern used by Sir Keith Holyoake when he opened the final link to Fox Glacier in 1965.
Hundreds more visitors and locals went to the Saturday market day at the Haast aerodrome to browse the stalls, chat with some of yester-years "rusty relics" - as the roadworkers who are now in their 70s and 80s were described - and watch the men work up a paddock with ageing machinery such as D8 dozers.
Yesterday, a memorial plaque was unveiled for popular Jackson Bay roadman Dan Greaney (1900-72).
It has been installed on a plinth at the Arawata Bridge.
Ms Nolan said the celebrations exceeded her expectations and she was extremely thankful to sponsors who had ensured the Dominie could fly in.
"It has been fabulous."
