Transport Minister Prajin Juntong expects Japan to start construction of new Bangkok-Chiang Mai and Kanchanaburi-Aranyaprathet rail lines next year.
He said on Monday that work could begin soon because both routes have been designed. He would seek cabinet approval on May 19 to sign a memorandum of cooperation with Japan later this month to proceed with construction.
The minister did not say when the rail lines would be completed.
The 670-kilometre Bangkok-Chiang Mai project route will be a high-speed railway.
The east-west route will be a double-track line stretching 574 kilometres from Kanchanaburi through Bangkok and Chachoengsao to the Laem Chabang port in Chon Buri province, and to Aranyaprathet district of Sa Kaeo province next to Cambodia.
Deputy Transport Minister Arkhom Termpittayapaisith discussed the projects with Hiroto Izumi, special adviser to the Japanese prime minister, at his ministry on Monday.
Mr Arkhom said the memorandum of cooperation would be signed in Tokyo on May 26 or 27. He added that Japanese officials would arrive in mid-June to survey route specifics. Investment plans would be finalised by year-end.
Japan would include its experience planning a Singapore-Malaysia railway project in its study on the Bangkok-Chiang Mai route, Mr Arkhom said. The Singapore-Malaysia project last week was postponed indefinitely beyond its 2020 completion date.
Japan promised to help Thailand develop relevant personnel and technologies, he said.
Also on Monday, ACM Prajin said China also wanted to start construction of its standard-gauge line from Bangkok via Kaeng Khoi district of Saraburi to Nakhon Ratchasima province in October or November.
That line is part of planned rail route linking China's Kunming province to Bangkok via Vientiane, Laos, slated for completion in 2019, ACM Prajin said.