Reaction in the US Congress to President Donald Trump's decision to withhold funding for the World Health Organization fell sharply along partisan lines on Wednesday, with Democrats calling it unconscionable and Republicans calling it the right move at the right time.

House Speaker Nancy Pelosi, a Democrat from California, described the decision in a written statement as "senseless".

"The President's halting of funding to the WHO as it leads the global fight against the coronavirus pandemic is senseless," Pelosi said in a written statement.

"We can only be successful in defeating this global pandemic through a coordinated international response with respect for science and data," Pelosi added.

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"But sadly, as he has since day one, the President is ignoring global health experts, disregarding science and undermining the heroes fighting on the front line, at great risk to the lives and livelihoods of Americans and people around the world," she wrote.

Trump accused the WHO of failing to adequately warn of the coronavirus and announced he would cut off US payments to the WHO in a briefing at the White House on Tuesday.

"The WHO failed in its basic duty and must be held accountable," Trump said.

Trump signalled that such a move was likely last week when he said the WHO had been "China-centric" in its handling of the coronavirus outbreak in January.

The WHO receives about $400m from the US each year, or about 8 percent of its $4.8bn annual budget.

"This decision is dangerous, illegal and will be swiftly challenged," Pelosi said without elaborating specifically on next steps.

The truth is a weak person, a poor leader, takes no responsibility. A weak person blames others. — Nancy Pelosi (@SpeakerPelosi) April 15, 2020

Congress and the White House appeared to differ on Wednesday on whether the law providing US funding for international organisations like the WHO, a United Nations agency, gives the president latitude to withhold the funds.

House Majority Leader Steny Hoyer, the number-two Democrat in the House, argued in a statement that Trump's decision was "unconscionable".

"This move will jeopardize the health of millions of people just as the southern hemisphere's virus season begins," Hoyer wrote.

"Surely, structural changes are needed at the World Health Organization to prevent it from being exploited by China and other countries for misinformation, but the way to do that is through engagement based on American leadership," Hoyer wrote.

Trump got support from Republican Senator Lindsey Graham who tweeted on Wednesday, "The current WHO leadership has proven to be incompetent and shown overwhelming evidence of China bias."

"Cutting off funding to the WHO at this time is the right move," Graham said.

The current WHO leadership has proven to be incompetent and shown overwhelming evidence of China bias.



Cutting off funding to the WHO at this time is the right move.https://t.co/DYv3QaSv20 — Lindsey Graham (@LindseyGrahamSC) April 15, 2020

Some politicians see Trump's move to cut off funds for WHO as an attempt to shift blame away from the president's own slow response to the virus.

Indeed, Trump was praising China's response to the Wuhan outbreak in February at the same time as the WHO was issuing statements in support of China's measures, which Trump is now criticising.

Democratic Senator Chris Murphy tweeted on Wednesday that Trump made an error when his administration refused WHO's help and decided to have the Centers for Disease Control produce tests for COVID-19 in the US.

"The WHO had produced 1.4 million tests by the end of February. We took none of them, because Trump decided to produce his own test, then botched the development and roll out," Murphy claimed.

"It wasn't the WHO that put us in the position we are today. It was our own President," Murphy tweeted.

Top Democrats in the US Senate laid out a plan on Wednesday to expand testing in the US. The plan, outlined by Senate Minority Leader Chuck Schumer, calls for a strategic plan to leverage a whole-of-society response with the allocation of emergency funding to enable rapid scaling up of testing.