A federal judge has blocked a Trump administration rule requiring immigrants to prove they will have health insurance or can afford medical care before they can get visas.

US District Judge Michael Simon, of Portland, Oregon, granted a nationwide temporary restraining order Saturday that prevented the rule from going into effect Sunday. It's not clear when he will rule on the merits of the case.

The ruling was the latest in a string of court decisions to derail White House initiatives aimed at limiting the admission of certain legal immigrants into the United States.

Seven US citizens and a nonprofit organization filed the federal lawsuit Wednesday charging that the health care requirement would block nearly two-thirds of all prospective legal immigrants.

The lawsuit also claimed the rule would greatly reduce or eliminate the number of immigrants who enter the US with family-sponsored visas.

'We're very grateful that the court recognized the need to block the health care ban immediately,' said Justice Action Center senior litigator Esther Sung, who argued at Saturday's hearing on behalf of the plaintiffs.

'The ban would separate families and cut two-thirds of green-card-based immigration starting tonight, were the ban not stopped.'

A federal judge in Portland, Oregon, has blocked a Trump administration rule that would require immigrants to prove they will have health insurance or can afford medical care before they can get visas. The Saturday ruling was the latest in a string of court decisions to derail President Donald Trump's initiatives aimed at limiting the admission of certain legal immigrants into the United States. Trump is seen outside the White House on Saturday night

The proclamation signed by President Donald Trump in early October applies to people seeking immigrant visas from abroad - not those in the US already.

It does not affect lawful permanent residents, nor does it apply to asylum-seekers, refugees or children.

The proclamation says immigrants will be barred from entering the country unless they are to be covered by health insurance within 30 days of entering or have enough financial resources to pay for any medical costs.

Trump had justified the policy on the grounds that immigrants were more likely to be uninsured, asserting that too many non-citizens were taking advantage of America's 'generous public health programs'.

Legal immigrants are three times as likely as American citizens to be uninsured, with uninsured rates of 23 percent to eight percent respectively, according to a study released by the Kaiser Family Foundation in February.

Trump said immigrants are contributing to the problem of 'uncompensated health care costs' that are 'passed on to the American people in the form of higher taxes, higher premiums, and higher fees for medical services'.

The rule is the Trump administration's latest effort to limit immigrant access to public programs while trying to move the country away from a family based immigration system to a merit-based system.

Seven US citizens and a nonprofit organization filed the federal lawsuit Wednesday charging that the health care requirement would block nearly two-thirds of all prospective legal immigrants. US visa holders are seen entering Texas from Mexico in June (file photo)

Under the government's visa rule, the required insurance can be bought individually or provided by an employer and it can be short-term coverage or catastrophic.

Medicaid doesn't count, and an immigrant can't get a visa if using the Affordable Care Act's subsidies when buying insurance. The federal government pays for those subsidies.

According to the Migration Policy Institute, a nonpartisan immigration think tank, 57 percent of US immigrants had private health insurance in 2017, compared with 69 percent of US-born, and 30 percent had public health insurance coverage, compared with 36 percent of native-born.

The uninsured rate for immigrants dropped from 32 percent to 20 percent from 2013 to 2017, since the implementation of the Affordable Care Act, according to Migration Policy.

There are about 1.1 million people who obtain green cards each year.

'Countless thousands across the country can breathe a sigh of relief today because the court recognized the urgent and irreparable harm that would have been inflicted' without the hold, said Jesse Bless, director of federal litigation at the American Immigration Lawyers Association.

Earlier this year, the administration made sweeping changes to regulations that would deny green cards to immigrants who use some forms of public assistance, but the courts have blocked that measure.