The United Nations' top human rights official condemned Hungary on Thursday for its "callous" treatment of migrants from the Middle East when its border police officers used tear gas, pepper spray and high-pressure water cannons to drive away the refugees.

In a statement, UN High Commissioner for Human Rights Zeid Ra'ad Al Hussein said he was "appalled" by how the Hungarian government used force to prevent refugees who were trying to break through a razor-wire fence along the Serbian border.

"The images of women and young children being assaulted with tear gas and water cannons at Hungary's border with Serbia were truly shocking," Zeid said.

He also accused Hungarian authorities of violating international law by using violence against the refugees, and even against journalists who were covering the incident.

"I am appalled at the callous, and in some cases illegal, actions of the Hungarian authorities in recent days, which include denying entry to, arresting, summarily rejecting and returning refugees, using disproportionate force on migrants and refugees, as well as reportedly assaulting journalists and seizing video documentation. Some of these actions amount to clear violations of international law," Zeid said.

At least two asylum seekers were reportedly seriously hurt during their encounter with Hungarian border police, with over 300 others needing medical attention. Two children were also flung over the fence to escape the mayhem.

After the violent incident, the Hungarian government built a fence on its border with Serbia. On Tuesday, Hungary also enacted a new law criminalising illegal entry.

Hungarian Prime Minister Victor Orban came to his country's defence, saying Hungary and its government were just "defending our lifestyle."

The UN human rights chief, however, attributed the current Hungarian policy on refugees to anti-Muslim sentiment.

"The package of measures brought in overnight between Monday and Tuesday is incompatible with the human rights commitments binding on Hungary," Zeid said.

"This is an entirely unacceptable infringement of the human rights of refugees and migrants. Seeking asylum is not a crime, and neither is entering a country irregularly," he added.