Sunai Phasuk, a senior researcher on Thailand for the New York-based organisation, on Tuesday expressed concern about the safety of these people if the plan is implemented.
The best solution to the problem was to find third countries for resettlement, but that faced difficulties because other nations were reluctant to accept them, he said.
Thailand has detained about 1,700 Rohingya boat people, mostly at immigration offices and social welfare shelters in the far South, and another 300 are already on the run from the camps - with a fresh escape reported overnight in Sadao, Songkhla.
Social Development and Human Security Minister Paveena Hongsakula recently floated the idea of moving them all to camps in Suan Phueng district of Ratchaburi province and Mae Sot district in Tak.
The idea was sharply opposed by the local people in the two provinces last week, as they were concerned about an added burden after already housing Karen people from Myanmar.
Human Rights Watch called for the release of the Rohingya because of worries about "inhumane and unsafe conditions''.
"Some senior Thai officials have recognised the Rohingya's plight, but they are still considering proposals that would keep them detained," said Brad Adams, Asia director at Human Rights Watch, in a statement also released on Tuesday.
"The Thai government needs to end the inhumane detention of Rohingya and ensure the United Nations refugee agency and other international organisations have full access to provide much needed protection and assistance."
Thai authorities have insisted the rights of the Rohingya in detention are being respected.
Thailand is trying to persuade Myanmar to allow them to go back, but the Myanmar government says it first needs to verify that they fled from Rakkhine state, where there has been inter-ethnic violence, not other countries.
Foreign Minister Surapong Tovichakchaikul urged Myanmar Foreign Minister Wunna Muang Lwin in talks last Wednesday in Hua Hin to speed up the process after the six-month time frame for them to stay as illegal migrants had passed.
The Muslim Rohingya fled ethnic clashes with the Buddhists in Rakkhine, mainly leaving for other countries by boat.
As the monsoon season will end in October, Mr Sunai expected more arrivals of boat people fleeing across the Andaman Sea.
About 100 police and defence volunteers were on Tuesday hunting 84 Rohingya migrants who broke out of their detention centre at the immigration office in Sadao district of Songkhla province overnight, reports said.
Of the total of 137 Rohingya migrants held at the centre, 86 escaped on Monday night.
They used used files to cut iron bars in their cell, broke through the ceiling, used sarongs as ropes to scale down the eight metres from the roof top of the second floor and then fled into the rubber plantation behind the immigration office building.
Two of them had since been recaptured, reports said.
It was the second break out this month. On the night of Aug 9, 30 Rohingya migrants broke out of their detention cell at the Sadao district police station and escaped. They are still free.