California Governor Gavin Newsom declared a statewide emergency to deal with the virus on Wednesday. AP

The US death toll from coronavirus infections rose to 11 on Wednesday as new cases emerged around New York City and Los Angeles, while Seattle-area health officials discouraged social gatherings amid the nation's largest outbreak.

The first California death from the virus was an elderly person in Placer County, near Sacramento, health officials said. The person had underlying health problems and likely had been exposed on a cruise ship voyage between San Francisco and Mexico last month.

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It was the first coronavirus fatality in the United States outside of Washington state, where 10 people have died in a cluster of at least 39 infections that have emerged through community transmission of the virus in two Seattle-area counties.

Although the Placer County patient who died was not believed to have contracted the virus locally, that case and a previous one from the San Francisco Bay Area linked to the same ocean liner have led health authorities to seek other cruise passengers who may have had close contact with those two individuals.

Ambulances are seen in a staging area at the North Kirkland Community Center in Kirkland, Washington. Reuters

Hours after the person's death was announced, California Governor Gavin Newsom declared a statewide emergency in response to the coronavirus, which he said has resulted in 53 cases across the nation's most populous state.

"The State of California is deploying every level of government to help identify cases and slow the spread of this coronavirus," Newsom said in a statement.

Newsom said the cruise ship, named the Grand Princess, had later sailed on to Hawaii and was returning to San Francisco, but would not be allowed into port until passengers had been tested for the virus.

"We are holding that ship off the coast," Newsom said.

Customers look at sanitizing wipes on the shelves of a pharmacy in New York. Marshall Ritzel/AP

Six new coronavirus patients were confirmed in Los Angeles County, public health officials said on Wednesday. One was a federal contractor who may have been exposed while conducting medical screenings at Los Angeles International Airport, the US Department of Homeland Security reported.

Three others likely were infected while traveling recently to northern Italy, one of the areas hardest hit in the global outbreak. Of the six in Los Angeles County, only one has been hospitalized. The other five are recovering in home isolation.

The greater Seattle region represents the biggest concentration of cases detected in the United States from a virus that has killed more than 3,000 people worldwide, mostly in China, where the epidemic originated in December.

Health officials check students' temperatures before their exams, amid fears about the spread of the COVID-19. AP

With most of the Seattle-area cases not linked to travel or exposure to people who might have been infected abroad, that means the virus has gone from being an imported phenomenon to taking up residence in Washington state, health officials say.

At least 18 cases, including six deaths, were connected to a long-term nursing facility for the elderly, called LifeCare Center of Kirkland, in a Seattle suburb.

Reuters