US President Donald Trump declared a national emergency on Friday because of the coronavirus outbreak across the nation.

"To unleash the full power of the federal government in this effort today, I am officially declaring a national emergency. Two very big words. The action I am taking will open up access to up to $50 billion - a very important and a large amount for states and territories or localities in our shared fight against this disease," he said.

Making the announcement at a news conference, the US President urged every state to set up emergency centers to help fight the virus.

Trump said the federal government was partnering with the private sector to accelerate production of test kits to make them more widely available to Americans.

He said there will be about 5 million coronavirus tests available but doubted that many will be needed.

"We still have a long way to go. There will be many more cases. But we'll take care of that," said Anthony Fauci, the National Institutes of Health expert who is on Trump's coronavirus task force.