Belgrade authorities are moving the some 1,000 Gypsies, or Roma, to four segregated metal container settlements outside of the city.
The families were packed onto dozens of buses, and their belongings - beds, wood stows and clothing - loaded onto trucks. Many could be heard loudly protesting, some shed tears, while others appeared happy to leave the drab and dirt-filled settlement.
Amnesty International said "people are coming up to us, with tears in their eyes, asking us what they should do and where they should go."
A pregnant 17-year-old girl has been told she will be sent to the town of Nis in southern Serbia, where she has no home, and nowhere to stay, the rights group added in a statement.
Amnesty said the "forced eviction" represents a "blatant" breach of human rights law.
"The Serbian government is flagrantly violating international law by allowing Belgrade city authorities to carry out this eviction," said John Dalhuisen, Amnesty International's Europe and Central Asia Director. In a statement, the group called for the European Commission to "immediately call on the city authorities" to stop the action.
Belgrade authorities say the settlement, built from wooden shacks in a new part of Belgrade, is illegal and prevents construction projects. It has been expanding for several years, as gypsies who have been resettled in other parts of the capital have gradually returned.
The settlement is on a field in front of a luxury hotel, while a new 10-floor housing complex - called Belvil - is some 100 meters (yards) away. The developers have complained that they cannot sell the apartments in the project while the slum remains.
Belgrade Mayor Dragan Djilas, who has faced criticism over Roma evictions in the past, defended the policy, saying the Roma would be better off in the new settlement than in the slum.
He said the Roma situation all over Europe is problematic, but Belgrade is doing its best. "We are trying to move things forward," he said.
Amnesty said it is likely that the metal containers the Roma are being moved to do not meet international adequate housing standards.
Although they have been able to take their belongings, the rights group said the community has not been allowed to take the scrap materials from which they earn their living, and have been told that they cannot collect or store scrap at the new sites.
The European Union has promised €3.5 million ($4.6 million) for permanent housing solutions for the Gypsies, Amnesty International said.
There are an estimated 500,000 Gypsies - many of them who resettled during the wars in the Balkans in the 1990s - living in Serbia, or about 7 percent of the population. They often face harassment from Serbian extreme nationalist groups.