Residents in the Vietnamese capital Hanoi also felt buildings sway.
“The ceiling lights were shaking quite strongly. I felt dizzy and scared,” said Hanoi resident Tran Hoa Phuong, who felt the earthquake in her 27-storey apartment building.
It hit about three hours after a 5.7-magnitude earthquake struck the same region of Laos, near the site of the large Xayaburi dam project.
Information is slow to trickle out of the closed communist state, and there were no reports of damage or injuries after the twin quakes early Thursday.
Pope Francis arrived in Bangkok on Wednesday and has a busy agenda Thursday meeting officials and the Thai king before he leads a mass in the evening.
There was no word from his team on whether he felt the quake.