"It is a welcome action on the part of the government," Jehan Perera, executive director of the National Peace Council of Sri Lanka, an advocacy NGO based in Colombo, told IRIN. "It is timely and it is something which should have happened earlier, but nonetheless we welcome it."
The government declared last month that there would be freedom of movement for more than 100,000 people remaining in the overcrowded, state-run camps, which it calls "welfare villages" and reiterated the promise on 30 November.
"The villages will be declared as open from this day ... The government has declared that any civilian will be free to leave the villages once they have given their personal details to the authorities concerned," according to the 30 November statement.
UN spokesman Gordon Weiss said the IDPs had been given 10 days to return to the camps if they leave.
“Around midday almost 6,000 people were able to leave the camps. It’s progressing in an orderly fashion,” Weiss told IRIN.
"It's a big step from people being confined to the camps,” he added.
Weiss said the IDPs are registered and provided with tokens when they leave the camps, which they would hand back upon their return.
"It serves a dual purpose. They will try to keep track of people and to make sure camps are not visited by some people who shouldn't be there," he said.
Nearly 280,000 people who fled the fighting in the final months of the country's bitter civil war this year entered the camps, which were hastily erected as the conflict ended in May.
Under intense pressure from the international community, the government in recent weeks has expedited the process of releasing IDPs, who have either returned to their places of origin or resettled elsewhere.
According to the latest Joint Humanitarian Update on 19 November, 136,242 people remain in the camps in the northeast, while 112,209 have been returned to their places of origin and 27,663 have been released to host families or into the care of elders.
Weiss said he expected a significant number of people would remain in the camps despite their opening today, but that many were expected to return to their places of origin in the next few months.
"The return process is not without problems. It's a lot of people to send back in a short period of time, and areas are not always prepared, but it's been going reasonably well," he said.
Concerns have been raised over the fate of returnees to war-torn areas, with NGOs calling for better support for the IDPs, and better access for humanitarian actors to the areas of return.
"The infrastructure is in a state of destruction and disrepair. [The IDPs] are released with hardly any resources, and the resources that are provided to them need to be supplemented and increased," said Perera of the National Peace Council.