US President Donald Trump has floated the idea of replacing a visa program for foreign investors with a so-called "gold card" that could be bought for US$5 million (HK$39 million) as a route to American citizenship.

Trump said he will replace the EB-5 immigrant investor visa program, which allows foreign investors of large sums of money that create or preserve US jobs to become permanent residents, with a so-called "gold card."

The EB-5 program grants "green cards" to foreigners promising to invest in US businesses.

"We are going to be selling a gold card," Trump said. "We are going to be putting a price on that card of about US$5 million," he added.

"It's going to give you green card privileges plus its going to be a route to (American) citizenship, and wealthy people would be coming into our country by buying this card," Trump said, adding that details about the scheme will come out in two weeks.

Trump added it is possible Russian oligarchs could qualify for the gold cards, when asked if those people would be eligible. "Yeah, possibly. Hey. I know some Russian oligarchs that are very nice people," he said.

The EB-5 Immigrant Investor Program, administered by the US Citizenship and Immigration Services, was created by Congress in 1990 to "stimulate the US economy through job creation and capital investment by foreign investors," according to the USCIS website.

"The EB-5 program ... it was full of nonsense, make believe and fraud, and it was a way to get a green card that was low price. So the president said, rather than having this sort of ridiculous EB-5 program, we're going to end the EB-5 program. We're going to replace it with the Trump gold card," Commerce Secretary Howard Lutnick said on Tuesday.

Meanwhile, Pacific microstate Nauru said it is selling citizenship to fund its retreat from rising seas, opening a contentious "golden passport" scheme as other climate financing runs dry.

The low-lying island nation of around 13,000 residents and a total landmass of just 21 square kilometers is planning a mass inland relocation as creeping seas start to eat away at its fertile coastal fringe. Researchers today estimate 80 percent of Nauru has been rendered uninhabitable by mining.

It will drum up funding by selling passports to foreigners for US$105,000 each, despite fears such schemes are ripe for criminal exploitation.

Reuters, Agence France-Presse

People stand on the steps of the US Citizenship and Immigration Services offices in New York. Reuters

Trump floats US$5m 'gold card' path to citizenship