US President Donald Trump said Monday he was in close contact with Chinese officials and offered any help that is necessary" to fight the coronavirus outbreak in China.

"We are in Very close communication with China concerning the virus," Trump said in a tweet. "Very few cases reported in the USA, but strongly on watch. We have offered China and President Xi any help that is necessary. Our experts are extraordinary!"

In early trading Monday, the Dow Jones Industrial Average fell 424 points, or 1.5 percent. By midday, the market had regained about 50 points, but still remained down about 1.28 percent. Investors bought bonds as a safe haven.

Airline, cruise and hotel stocks dropped on fears that the virus could limit global travel.

Officials in China said there are now about 2,800 confirmed cases of the coronavirus and the death toll has risen to 81. The elderly and infirm are most vulnerable to the flu-like disease.

Bloomberg news reported that China's markets will remain closed until Feb 3 after officials extended the Lunar New Year break three days as part of the effort to contain the virus. Trading will resume next Monday in Shanghai and Shenzhen, but authorities advised that most companies shouldn't resume work until at least Feb 9.

China's government has imposed strict limits on travel in Hubei province where the outbreak was detected and the US Centers for Disease Control and Prevention (CDC) warned travelers to stay away from that part of China.

Dr Paul Stoffels, Johnson & Johnson's chief scientific officer, said the drug-maker can develop a vaccine in a few months to fight the coronavirus but that it could take as much as a year to bring it to market.

"We have dozens of scientists working on this so we're pretty confident we can get something made that will work and stay active for the longer term," he told CNBC. "We'll see in the next few weeks how this goes."

In the US, five travelers from Wuhan have been confirmed to have been infected with the virus in Arizona, California, Illinois and Washington state. The virus has also spread from China to other Asian countries, including Japan, South Korea, Thailand and Singapore.

"Person-to-person spread in the United States has not yet been detected, but it's likely to occur to some extent," the CDC said in an advisory posted to its website. "It's important to note that person-to-person spread can happen on a continuum. Some viruses are highly contagious — like measles — while other viruses are less so. It's important to know that in order to assess the risk posed by this virus."

Nevertheless, the CDC said more cases in the US are "likely" to be detected, including in the US. The virus could be spread person-to-person and it "would not be surprising" if the virus were spread in some hospitals.

The CDC is screening passengers on direct and connecting flights from Wuhan at five major airports: Atlanta, Chicago, Los Angeles, San Francisco and New York.

CDC teams have been sent to Illinois and Washington state to assist in on-going investigations of the virus.

The CDC recommends getting a flu shot and taking routine preventative actions such as frequent and vigorous hand-washing, especially after going into public places or riding public transportation.

On Sunday, the US State Department said it will organize a single flight to evacuate diplomats and a few private citizens from the central China city of Wuhan where the virus broke out last month. The plane is expected to leave Tuesday and fly to San Francisco.

The coronaviruses are named for the crown-like spikes on their surfaces. Most infections are limited to animals, including pigs and cats. In recent years, the coronaviruses have caused worldwide outbreak among humans, but officials don't know how easily the current strain of the virus is spread between people, the CDC said.

Researchers have identified seven strains of the virus known to infect humans. Most strains lead to common colds, but two are known to be deadly and cause Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS), the CDC said.