The 50m deep sinkhole extended about 900sq m in front of the Vajira Hospital, halting traffic.
Footage on social media showed the road slowly sinking as water poured out from a drainage pipe, dragging down electricity poles. The hospital announced that it would not take on patients during the incident.
"Dirt from an underground train construction was sliding in," Prime Minister Anutin Charnvirakul said. "Luckily there are no deaths or injuries."
Bangkok Governor Chadchart Sittipunt said a pipe had burst so water and power lines have also been cut.
"The hospital has no problems, but we are worried about the police station: that's still dangerous and the public has been evacuated," he said.
By noon, authorities said they had halted further ground movement and were monitoring the site closely.
