Caretaker Transport Minister Chatchart Sittipunt said the biggest damage occurred at the 151 kilometre mark on Highway 118, which links Chiang Rai and Chiang Mai.
The Highways Department has not closed the route. Traffic is being directed to a 300-metre detour around the major damage. The department is still monitoring the continuing aftershocks. More than 1,000 separate tremors have been recorded.
Two pedestrian flyovers have already been declared unsafe and will be demolished immediately, Mr Chatchart said. Inspectors were closely examining another 218 flyovers within a 50km-radious of the quake's epicentre.
Mr Chatchart said it was estimated that repairs to the road would take about two months.
He said the 100 million baht would come from the department’s annual budget. If it was insufficient the ministry would have to seek approval from the Election Commission to draw on funds from the government's contingency fund, the central budget.