Donald Trump has defended his administration's handling of the coronavirus crisis, saying his government is doing a "great" job, lashing out at Democrats and saying: "So far, by the way, we have not had one death."

Returning from a two-day trip to India, the president responded to a growing chorus of criticism, with even usually loyal Republican politicians questioning whether he is doing enough to protect Americans against the deadly virus.

Mr Trump tweeted: "CDC and my Administration are doing a GREAT job of handling Coronavirus, including the very early closing of our borders to certain areas of the world.

"It was opposed by the Dems, 'too soon', but turned out to be the correct decision. No matter how well we do, however, the Democrats talking point is that we are doing badly.

"If the virus disappeared tomorrow, they would say we did a really poor, and even incompetent, job. Not fair, but it is what it is. So far, by the way, we have not had one death. Let's keep it that way!"

Coronavirus: Streets around world left empty Show all 10 1 /10 Coronavirus: Streets around world left empty Coronavirus: Streets around world left empty A man wearing a face mask crosses a road in Wuhan, the epicentre of the novel coronavirus outbreak. Reuters Coronavirus: Streets around world left empty A view of the empty entrance to the UniversitÃ Cattolica (Catholic University) in Milan, northern Italy, on 24 February, 2020. EPA Coronavirus: Streets around world left empty Empty streets in Daegu, South Korea, on 23 February, 2020. EPA Coronavirus: Streets around world left empty Empty streets in Daegu, South Korea, on 23 February 2020. EPA Coronavirus: Streets around world left empty A lone sanitation worker sits near the closed Hankou Railway Station in Wuhan, Hubei province, China, on February 24, 2020. Reuters Coronavirus: Streets around world left empty A view of a deserted street in Codogno, northern Italy, on February 23, 2020. EPA Coronavirus: Streets around world left empty Italian police officers set a road block in Codogno, Northern Italy, on Monday, Feb. 24, 2020. AP Coronavirus: Streets around world left empty A supermarket closed in Codogno, one the northern Italian towns placed under lockdown, on February 23, 2020. EPA Coronavirus: Streets around world left empty A lone cyclist wearing sanitary masks pedals in the center of Codogno, Northern Italy. LaPresse via AP Coronavirus: Streets around world left empty An empty road at the entrance of the small Italian town of Codogno on February 23, 2020. AFP via Getty

Earlier, the US Centers for Disease Control and Prevention had outlined what schools and businesses would need to do if the coronavirus reaches pandemic levels, which officials say is likely.

"It's not so much of a question of if this will happen in this country any more but a question of when this will happen," Dr Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases, told reporters.

"We are asking the American public to prepare for the expectation that this might be bad."

There are currently 57 people in the United States with the virus. Many of the US cases are individuals returning to the country after vacationing onboard the Diamond Princess cruise liner, which was quarantined in Japan after passengers were found to be carrying the virus.

Worldwide there are more than 80,200 confirmed cases, the majority of them in China. There have been more than 2,700 deaths resulting from the new virus.

The city of San Francisco has declared a state of emergency, even though no cases have been reported there yet.

London Breed, mayor of the Californian city, announced the decision in a statement, saying "the global picture" surrounding the Wuhan coronavirus was "changing rapidly" and city officials "need to step-up preparedness".

"We see the virus spreading in new parts of the world every day," she continued, "and we are taking the necessary steps to protect San Franciscans from harm."

Both Republican and Democratic senators have questioned the amount of funding the White House is requesting to protect Americans.

Richard Shelby, a Republican senator from Alabama, told Health and Human Services Secretary Alex Azar that the outbreak "could be an existential threat to a lot of people in this country", adding: "If you low ball something like this, you'll pay for it later."

Democratic Senator Patty Murray of Washington said the administration's handling of the coronavirus was "unacceptable". "We cannot afford to plan on the cheap or at the last minute," she said.

Chad Wolf, the acting Homeland Security Secretary, was given a rough ride by senators including John Kennedy of Louisiana, a Republican usually loyal to Mr Trump, who asked "are you sure of that" when Mr Wolf wrongly claimed the mortality rate for coronavirus – about 2 per cent – is roughly the same as for flu. In fact it is about 100 times more deadly.

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Mr Worlf was also unable to answer a series of questions including how quickly the administration expected the virus to spread. Mr Kennedy told him: "You're secretary. I think you ought to know that answer."