A fundraising thermometer, unveiled at the launch, indicated $877,500 had been already been raised, after huge donations were made on the night.
The Aoraki Foundation provided $20,000, while Trust Aoraki Ltd provided $100,000 and the Twizel Wine Club provided $250,000.
The project would replace the town's existing facility, which was now outdated, with a modern medical centre, complete with six consulting rooms and a triage unit.
Mr Williamson said he was ''really encouraged'' the project had ongoing support.
''Being the most isolated medical centre in the country, and being 180km from a hospital, the need for a modern medical centre is paramount.
''This is the first purpose-built community-owned practice in South Canterbury for at least 20 years, and if anyone can do it, the high country can.''