All gates at the Commerce Ministry have been closed since 10am, following the arrival of anti-government protesters.
Some reporters were also denied access.
Protesters are now gathering outside the premise in Nonthaburi.
Permanent Secretary Srirat Rastapana said in a statement that all 4,000 officers inside the premise would be protected. There is no instruction for officers to leave office yet, pending for the protest situation.
"Tight security is in place at all gates," she said.
The Foreign Trade Department also announced that import/export certificates can still be issued by other offices at Bangkok Port, Suvarnabhumi Airport and Ratchadapisek.