HONOLULU, Hawaii - A US judge blocked most of US President Donald Trump's latest travel ban on Tuesday, just hours before it was set to take effect, saying the revised order "suffers from precisely the same maladies as its predecessor".

It was the third set of travel restrictions issued by the president to be thwarted, in whole or in part, by the courts.

Hawaii federal judge Derrick Watson issued the 40-page ruling after the ban on a set of mostly Muslim countries was challenged by the state, which warned that the restrictions would separate families and undermine the recruiting of diverse college students.

White House spokeswoman Sarah Huckabee Sanders called the ruling "dangerously flawed" and said it "undercuts the president's efforts to keep the American people safe". The Justice Department said it will quickly appeal.

At issue was a ban, announced in September and set to go into effect early on Wednesday, on travelers from Chad, Iran, Libya, the Democratic People's Republic of Korea, Somalia, Syria and Yemen, along with some Venezuelan government officials and their families.

The Trump administration said the ban was based on an assessment of each country's security situation and willingness to share information with the United States.

Watson, appointed to the bench by president Barack Obama, said the new restrictions ignore a federal appeals court ruling against Trump's previous ban.

The latest version "plainly discriminates based on nationality in the manner that the 9th Circuit has found antithetical to... the founding principles of this nation," Watson said.

The judge's ruling applies only to the six Muslim-majority countries on the list. It does not affect the restrictions against the DPRK or Venezuela, because Hawaii did not ask for that.

The ban aimed mostly at Muslim-majority countries has led to chaos and confusion at airports nationwide and triggered several lawsuits, including one from Hawaii.

Ap - Afp - Xinhua