The investment is to accommodate the launch of the Asean Economic Community (AEC) and economic expansion of the Greater Mekong Subregion (GMS).
The biggest investment in Thailand's history was announced by Prime Minister Yingluck Shinawatra in her opening address at the Thailand Investment Conference yesterday.
She said the GMS members are the key to connectivity and development in the Asean region.
The GMS comprises Yunnan and Guangxi provinces in China and the countries in the Mekong basin - Thailand, Cambodia, Laos, Myanmar and Vietnam. These five countries along with Yunnan and Guangxi cover 2.6 million square kilometres with a combined population of 326 million.
Ms Yingluck said GMS members have maintained steady economic cooperation and achieved considerable success in laying the foundations for economic cooperation.
During the fourth GMS summit held in Myanmar last December, leaders agreed that over the next two years they should cooperate to develop land transport to link trade and investment and to promote access to goods and services before the launch of the AEC in 2015.
The leaders also jointly announced a strategy for 2012-2022 to promote economic growth in the GMS region, which is a significant mechanism that will lead to closer cooperation in the third decade of the GMS grouping, Ms Yingluck said.
She stressed the need for connectivity in the region by creating supply chain and logistics systems.
She said Thailand, as an Asean hub, plays an important role in boosting connectivity and that the government plans to invest $90 billion in infrastructure projects such as the Thai-Lao high-speed train scheme and flood prevention and management projects.
A government source said the investment would cover seven years, while the main financial sources would come from borrowing.
Thailand will continue its proactive role in supporting the development of the GMS, Ms Yingluck said.
She said that government leaders in the GMS countries have collaborated closely to promote and strengthen economic ties.
Ms Yingluck said construction of major infrastructure projects in the region is getting under way. They include the Dawei deep-sea port in Myanmar and a project to build a highway to connect Dawei with Laem Chabang deep-sea port on Thailand's Eastern Seaboard.
Thailand has also begun urgent work to develop water management projects.
Ms Yingluck said GMS countries have geographical advantages as they are located between the Indian and the Pacific oceans, which link India and China.
The link between the Indian and the Pacific oceans will have significant implications in that it will increase the volume of trade and investment, which will bring great wealth to GMS countries, she said.
Meanwhile, Finance Minister Kittiratt Na-Ranong has urged state enterprises to make use of infrastructure investment opportunities in neighbouring countries.
He said state enterprises should be proactive in seeking opportunities rather than waiting for invitations from governments, especially for projects that would link regional logistics and transport systems.
"Since we have great potential to be the centre of a regional logistics system, we should try to make it happen," Mr Kittiratt said.
For example, as Myanmar plans to develop a deep-sea port at Dawei, the Port Authority of Thailand should study the possibility of joining in the project's investment, assessing its commercial viability, he said.
"This is not a policy; it is just an idea. I want state enterprises to consider these opportunities on their own, and if they are [ready to invest overseas], then go for it," Mr Kittiratt said.
Italian-Thai Development has a contract for Dawei, and Mr Kittiratt said the government is considering entering into a venture with the company.