The regions include popular tourist areas Chiang Mai, Phangnga, Krabi, Hua Hin, Pattaya, and Cha-am, and follow the successful reopening of Phuket and Samui islands to vaccinated people in pilot schemes since July.
The country is keen to welcome back foreign visitors, after nearly 18 months of strict entry policies that contributed to a collapse in tourism, a key sector that drew 40 million visitors in 2019.
Authorities will also reduce the quarantine time nationwide for visitors arriving from Oct 1, the Covid-19 task force said, halving it to seven days for vaccinated arrivals, and cutting it to 10 days for those not inoculated.
It will also further ease restrictions from Friday in 29 "dark red" provinces under maximum control, including Bangkok, to allow more businesses and activities to reopen, such as spas, libraries, cinemas, indoor sports venues and nail salons.
The easing of measures come as the country tries to increase the rate of vaccinations, after initial supply shortages. Less than a third of the population has been inoculated so far.
The task force also approved a plan to procure a combined 3.35 million doses of Covid-19 vaccines, although no delivery timeframe was provided.
Pending Cabinet approval, Thailand will seek to buy 2.79 million doses of the Pfizer and BioNTech vaccines and 165,000 AstraZeneca shots from Spain and 400,000 AstraZeneca doses sourced from Hungary, a spokesperson said.