U.S. President Donald Trump's immigration policies could lead to collective expulsions of migrants in a breach of international law, the United Nations human rights chief said on Wednesday.

Zeid Ra'ad al-Hussein, the U.N. High Commmissioner for Human Rights, also voiced concern at the new U.S. policy banning entry of people from six Muslim-majority countries for 90 days, announced on Monday after Trump's controversial first attempt was blocked in the courts.

Greater leadership was needed to address a surge in discrimination, anti-Semitism and violence against ethnic and religious minorities in the United States, he said in an annual speech to the United Nations Human Rights Council in Geneva.

"Vilification of entire groups such as Mexicans and Muslims, and false claims that migrants commit more crimes than U.S. citizens, are harmful and fuel xenophobic abuses," Zeid said.

He voiced dismay at "attempts by the President to intimidate or undermine journalists and judges".

The revised policies would greatly increase the number of migrants at immediate risk of deportation, regardless of the number of years spent in the United States or family roots, Zeid said.

"Expedited deportations could amount to collective expulsions and refoulement, in breach of international law, if undertaken without due process guarantees, including individual assessment," Zeid said, referring to the U.N. Refugee Convention that prohibits sending back people who are fleeing war, violence or persecution.

He was particularly concerned about the impact of children "who face being detained, or may see their families torn apart".