President Donald Trump on Monday said he planned to temporarily suspend immigration to the United States because of the coronavirus pandemic, despite the US already being the worst-hit country in the world.

"In light of the attack from the Invisible Enemy, as well as the need to protect the jobs of our GREAT American Citizens, I will be signing an Executive Order to temporarily suspend immigration into the United States!" he tweeted Monday night

In light of the attack from the Invisible Enemy, as well as the need to protect the jobs of our GREAT American Citizens, I will be signing an Executive Order to temporarily suspend immigration into the United States!

— Donald J. Trump (@realDonaldTrump) April 21, 2020

Trump said the move would also protect Americans’ jobs, though the pandemic crisis has already left millions in the US out of work.

The White House declined to offer further details about the reasoning behind the decision, its timing, or its legal basis.

"As our country battles the pandemic, as workers put their lives on the line, the President attacks immigrants & blames others for his own failures", former Democratic presidential candidate Amy Klobuchar said in a tweet.

Immigration is largely halted into the United States anyway thanks to border restrictions and flight bans put in place as the virus spread across the globe.

But the issue remains an effective rallying cry for Trump's supporters.

Trump won the White House in 2016 in part on a promise to curb immigration by building a wall on the US border with Mexico. He and his advisers have spent the first three years of his tenure cracking down on both legal and illegal entries into the country. Crowds regularly chant "Build the Wall!" at Trump's political rallies, which are now idled because of the virus.

Trump has lamented the economic fallout of the outbreak; his stewardship of the US economy was set to be his key argument for re-election in November.

The US death toll from the virus topped 42,000 on Monday, according to a Reuters tally.

The US economy has come to a near standstill because of the pandemic; more than 22 million people applied for unemployment benefits in the last month.

"You cut off immigration, you crater our nation’s already weakened economy," former Democratic presidential candidate Julian Castro said in a tweet. "What a dumb move."

The United States has the world's largest number of confirmed coronavirus cases, with more than 780,000 infections, up 27,000 on Monday.

But the president has made a point of saying the peak had passed and has been encouraging US states to reopen their economies.

"It makes sense to protect opportunities for our workforce while this pandemic plays out," said Thomas Homan, Trump's former acting director of US Immigration and Customs Enforcement. "It's really not about immigration. It's about the pandemic and keeping our country safer while protecting opportunities for unemployed Americans."

The United States in mid-March suspended all routine visa services, both immigrant and non-immigrant, in most countries worldwide due to the coronavirus outbreak in a move that has potentially impacted hundreds of thousands of people.

US missions have continued to provide emergency visa services as resources allowed and a senior State Department official in late March said US was ready work with people who were already identified as being eligible for various types of visas, including one for medical professionals.

The administration recently announced an easing of rules to allow in more agricultural workers on temporary H2A visas to help farmers with their crops.