Bangkok to the northeastern province of Nakhon Ratchasima, a distance of more than 250km, will start later this year and is scheduled for completion in 2021.
It will cost an estimated 179 billion baht (around US$5.1 billion).
The government hopes to eventually extend the high-speed railway by some 350km to Nong Khai Province, opposite Laos, in the hope of boosting cross-border trade volume and turning Thailand into a regional hub.
It could eventually link Bangkok and China’s southwestern city of Kunming, over 1,200 km away, via landlocked Laos.
China, as part of its “One Belt, One Road initiative” to link Asia with Europe, is already constructing a 417-km stretch of single-track railway through Laos as part of a planned regional railway network linking Kunming with Singapore via Laos, Thailand and Malaysia.