Both United States Democratic presidential candidates on Thursday lashed out at US President Donald Trump's response to the coronavirus outbreak as woefully insufficient to date, and put forth their own plans for dealing with the pandemic.

In a speech delivered from his hometown of Wilmington, Delaware, frontrunner Joe Biden said the Trump administration has so far shown itself unable to cope with the unfolding crisis.

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"No president can promise to prevent future outbreaks, but I can promise you this, when I'm president we will be better prepared, respond better and recover better," Biden said. "We will lead with science, listen to the experts, [we] will heed their advice. We'll build American leadership and rebuild it to rally the world to meet the global threats that we are likely to face again."

Biden cautioned that the virus, which some Trump allies have dismissed as overblown fodder for the president's critics, "does not have a political affiliation". And in a direct dig at Trump, he added another pledge: "I'll always tell you the truth. This is the responsibility of a president. That's what is owed the American people."

Biden released a detailed plan, which he said Trump is "welcome to adopt", that called for wide availability of free testing, free preventive care and treatment of the disease associated with the virus, COVID-19. The plan also called for rapid development of a vaccine, and full deployment of the necessary supplies, personnel and facilities to stem the outbreak.

The former vice president also pressed for economic measures to mitigate the impact of the outbreak, including offering emergency paid leave for all those impacted by the coronavirus, assistance for small businesses and employees who have been affected, and debt relief for homeowners and students with loans they may not be able to pay in the short term.

Federal resources, he said, should be mobilised to ensure at least 10 testing sites in every state, and federal aid - including from the Pentagon - should be provided to put a stand-up hospital in any US city where an outbreak exceeds the capacity of existing healthcare infrastructure.

Biden also pledged that his administration would hold daily briefings in any such crisis, with top public health professionals in front of cameras to address the nation directly.

Democratic presidential candidate Bernie Sanders speaks to reporters about coronavirus Thursday in Burlington, Vermont [Charles Krupa/AP Photo]

Speaking just a couple hours later, Sanders said Trump should declare a national emergency and said a hotline should be established for people seeking information about the virus. He also said the US was at a "major disadvantage" compared with other countries since many people have no medical insurance.

Sanders has advocated for fully government-financed healthcare under a Medicare for All system that is the centrepiece of his campaign. But he said Thursday that in the meantime during the outbreak, the government must ensure that, "Everyone must be able to get all of the healthcare that they need without cost." He added that if a vaccine for the virus is developed, it should be free.

"We need an emergency response to the emergency," Sanders said, "and we need it immediately."

Biden and Sanders have both cancelled public events in advance of next Tuesday's primaries, yielding to public health officers and elected officials who are discouraging large campaign rallies. The pair will meet in a debate Sunday night on CNN, without a live audience, which organisers on Thursday said they were moving from Arizona to Washington, DC to minimise travel for the candidates and their staff.