The US Supreme Court has allowed Donald Trump to bar scores of Central American migrants from seeking refuge in the US while legal challenges to the policy progress.

The Trump administration announced in July that most migrants who traveled through a country other than their homeland to reach America and failed to claim asylum there would be denied entry.

It effectively bars almost all asylum seekers from Honduras, El Salvador and Guatemala. Mexicans are unaffected given their country borders the US.

More than 400,000 people from those three countries were caught illegally crossing the US-Mexico border this year, a key driver of the sharp recent rise in border arrests.

A judge in a lower court had blocked the policy from being implemented, but the Supreme Court has allowed it to go ahead for now, while legal challenges work their way through the courts.