The initiative aims to pave the way for talks between warring camps in Myanmar.
But critics say the aid will only help the junta as the majority of displaced people may not be able to access it.
U.N. Special Rapporteur on the situation of human rights in Myanmar, Tom Andrews, discussed the plan on March 20.
"The problem that we have right now is that humanitarian aid is not going to the areas that need it most. And I'm talking about the conflict areas, the areas outside of SAK-administered areas of the country. This is the fastest-growing part of the country. That is where most of the people, growing numbers of people, in the country that need humanitarian aid are."
Myanmar has been locked in conflict since the military seized power in 2021, upending a decade of tentative democracy and reform.
At least 2.6 million people have been displaced by fighting, according to the U.N., and more than 18 million people are in need of assistance.
Thailand's foreign ministry said the first batch of relief bags carry rice, dried food, and other essentials for 20,000 people.
It was delivered in a convoy by the Thai Red Cross to its Myanmar counterpart at the Mae Sot-Myawaddy border crossing.
And will be distributed in three pilot locations, observed by ASEAN's humanitarian and disaster agency.
The project is part of a wider peace initiative by Thailand to establish a humanitarian corridor as a civil war intensifies between Myanmar's military on one side and ethnic minority armies and a resistance movement on the other.
