WASHINGTON - More than 800 American experts and organisations in public health and law have jointly signed an open letter to United States Vice-President Mike Pence, calling for a government response to provide support and effectively manage the coronavirus outbreak.

Sustained human-to-human transmission of the coronavirus, which causes the Covid-19 disease, in the US appears to be inevitable, experts said in the letter.

The death toll from coronavirus in the US rose to 12 on Thursday, with 53 new cases reported across the country, bringing the total cases to 230.

In the letter, the experts called for adequate funding and support for the response while noting the safety of healthcare workers and other first responders to the epidemic should be guaranteed.

The experts said it will be critical for policymakers to ensure comprehensive and affordable access to testing, including for the uninsured.

"Policymakers must work directly with insurance companies to allow all insured individuals to adhere to public health recommendations," they said.

The experts also stressed the importance of transparent and timely reporting of the epidemic situation in maintaining public trust and cooperation.

"Science needs to guide messaging to the public, and no government official should make misleading or unfounded statements, nor pressure others to do so," the letter said.

"Clear, coherent, and uncontradictory messaging based on the best science will improve compliance and effectiveness of voluntary self-isolation, and other voluntary social distancing measures."

They also stressed the importance of allowing people to voluntarily cooperate with public health advice about prevention, providing robust social and economic support and clear education.

"Where social distancing measures are recommended, the government and relevant institutions should help ensure that people are in a position to comply, without excessive or unfairly distributed hardship."

Policymakers should base decisions on social distancing measures and closures on the best available science, they said. Employers, institutions, and schools should proactively determine adaptations and accommodations for closures such as virtual education.

Mr Pence said on Tuesday that both Medicaid and Medicare programmes would cover the costs of the tests for those enrolled.

On Thursday, Congress approved more than US$8 billion (S$11 billion) to fight the outbreak.