The frigate HTMS Bhumibol Adulyadej was reported to be escorting the cruise ship Westerdam to an undisclosed port in Thailand to disembark its passengers.
Lydia Miller, a Twitter account member with the name of @Pebblecovefarm, on Wednesday posted a picture of the frigate, apparently taken from the cruise vessel.
"Captain announced we are now being escorted by this Navy ship to an anchorage spot off the coast of Thailand, where we’ll get fuel and provisions and continue disembarkation process," the account member tweeted.
The Westerdam with 1,455 tourists and 802 crew on board was off the coast in the Gulf of Thailand on Wednesday night, according to vesselfinder.com, a website that tracks movements of all ships.
The Holland America Line, which operates the ship, said on Wednesday Cambodia has agreed to let the cruise ship to dock at the Cambodian sea port of Sihanoukville on Thursday.
The shipping line announced on Monday that it would let all people alight at Laem Chabang deep-sea port in Chon Buri and leave for home after disembarkation.
However, the government will not allow the gigantic ship to dock ion Thailand due to fears over the coronavirus.
There was no comment from the navy on the frigate's mission.
A Marine Department statement released on Wednesday reiterated the ship had not applied for permission to enter Thai waters.
The Thai Maritime Enforcement Command Centre said it planned to order the Westerdam to moor off the Thai coast and would supply fuel, food, medicines and other staples so that it would "safely arrive at its final destination".
Prime Minister Prayut Chan-o-cha said on Tuesday the government would give humanitarian help to the Dutch-flagged vessel.
The ship started its journey in Singapore on Jan 16 and it was not allowed to make ports of call in the Philippines, Taiwan, Guam and Japan and Okinawa after it left virus-hit Hong Kong on Feb 1, due to fears of contagion with the deadly virus.
It was unclear whether there were any cases among the people on the ship