Thailand's army chief Prayuth Chan-ocha has called for a meeting with permanent secretaries at 2pm local time (3pm Singapore time).
In what appears to be a move to forestall unrest in other parts of Thailand, a similar meeting has also been called in the north, northeast and southern Thailand.
The caretaker Cabinet, caught off-guard, is also holding an emergency meeting on Tuesday in a "safe house", according to the National News Bureau of Thailand.
Both sides of the political conflict appear to be taking a wait-and-see attitude as the army's intentions unfold by the hour.
Citing a worsening security situation, General Prayuth declared martial law in Thailand starting at 3am local time on Tuesday morning.
Martial law which puts security in the hands of the army with sweeping powers to detain people, does not amount to a coup d'etat, but is likely to be seen as such by the pro-government camp - unless any crackdowns are even handed and target both pro- and anti-government camps.
An announcement on military-run television said martial law had been declared "to restore peace and order for people from all sides", stressing that the move "is not a coup".
"The public do not need to panic but can still live their lives as normal," it added.
Army tanks, Humvees and trucks rolled into streets ofBangkok on Tuesday morning, setting up checkpoints and partial roadblocks that created snaking queues in various parts of the capital.
