Children have been separated from their families by police in chaotic scenes as migrants broke through Serbia's border with Hungary, Amnesty International says.
The rights group says at least nine people, including at least four children, were separated by Hungarian police after migrants surged forward and broke through a border fence and the police responded with pepper spray, causing panic.
"The families are desperate to be reunited with their children. Not only have they experienced the traumatic journey to the border and the use of force by the police, they have now lost the security of being with their parents," crisis response director Tirana Hassan said in a statement from the scene.
The rights group says the children are thought to have been brought to a nearby border control building.
"The Hungarian authorities must immediately hand these children over to their families," Hassan said.
The violence broke out after hundreds of people became frustrated at Hungary's closure of its border, previously a major crossing-point into Europe for migrants and refugees fleeing war in Syria and elsewhere and a flashpoint in Europe's refugee crisis.
The situation escalated and there were clashes between riot police and migrants, as police fired tear gas and water cannon and migrants threw sticks, stones and bottles.
Some migrants managed to pull down wire mesh and run into Hungary.
A father of an eight-year-old boy told Amnesty his child was taken from him as he was holding his hand and they have been separated ever since.
Amnesty says another man was searching for two children aged six and eight, and that eyewitnesses had seen Hungarian police pick up a mother and child and take them away.