A Hawaii federal judge has halted US President Donal Trump’s revised travel ban just hours before it was due to come into force.

The decision by US District Judge Derrick Watson blocks a 90-day ban on new visa approvals for people from six Muslim-majority nations.

The new order would ban all immigrants or non-immigrant entry of citizens from Syria, Yemen, Sudan, Somalia, Iran and Libya.

Trump, who was addressing a supporters rally as news of the judgment broke, branded it “an unprecedented judicial overreach” and vowed to appeal the decision in court.

“This ruling makes us look weak, which by the way we no longer are. We’re going to fight this terrible ruling,” he said.

Last month crew union Nautilus International has warned about the effects of Trump’s executive order on seafarers calling at the US.

General secretary Mark Dickinson wrote to UK foreign secretary Boris Johnson, urging him to seek clarification on UK crew rights.

He expressed “deep concern” over the move and said he was “disturbed” at the implications.

“There are serious safety and welfare issues at stake if seafarers are unable to join or leave their ships as planned,” the letter says.

Nautilus said some owners are already being advised not to attempt crew changes in the US involving people from the affected countries

And the union fears already restrictive shore leave policies look set to become “even more extreme”

Nautilus points out that special protection for seafarers on shore leave, repatriation, transit and transfer is enshrined in the ILO 185 convention.

However, the Standard P&I Club has said that it does not believe ships carrying crew from the affected countries are being denied entry into US ports.