The workers - most of whom travelled from Bangkok and other provinces where they work and stay - stood patiently in a queue longer than 300 metres to go through the immigration procedure.
Songkran Festival, from April 11-17, is also celebrated in Myanmar, Laos and Cambodia.
Many Cambodian workers - many of whom only return home once a year during Songkran - also got on board public transport vans from Pathum Thani's Rangsit area on Thursday to spend the long holidays with their families and relatives in Cambodia.