A Foreign Ministry source said the countries included China, the United States, Britain, Israel and the Philippines, as well as the Hong Kong special economic zone.
Hong Kong executive director of the Travel Industry Council, Joseph Tung Yao-chung, warned Hong Kong tourists to avoid protests and crowded areas.
The travel alert for Hong Kong travellers remains at amber — the lowest of the three-level alert system.
He said about 500 Hong Kong tourists were touring Thailand.
UK Minister of State for the Foreign and Commonwealth office, Hugo Swire, said he took heart from the army's assurance that the invocation of martial law is not a coup.
"We expect them to remain true to their word. I call on the military to act in accordance with international human rights standards and the rule of law, and respect democratic principles and institutions,'' he said.
New Zealand's Foreign Affairs and Trade Ministry spokesman advised the 990 New Zealand nationals currently in Thailand to avoid all rallies, demonstrations and large public gatherings.
Israel's Foreign Ministry warned Israelis here to avoid protest zones and to stay away from areas where security forces are concentrated.
United Nations secretary-general Ban Ki-moon reiterated his call on all parties to exercise "utmost restraint" in the wake of the army’s martial law declaration.
Canada's Foreign Affairs Minister John Baird said yesterday Canada remains deeply concerned by the crisis.
All parties must resolve their differences peacefully through dialogue, while respecting democratic principles and the rule of law, he said.