NEW YORK - A patient at a New York City hospital has been isolated and is now undergoing medical tests for possible Ebola virus, health official said on Monday.

"Odds are this is not Ebola," said Jeremy Boal, chief medical officer at Mount Sinai Health System in Manhattan. "It's much more likely that this is a much more common condition."

Blood samples have been sent to the Centers for Disease Control and Protection (CDC) in Atlanta and results are expected in 24 to 48 hours, Boal said.

The New York City Department of Health and Mental Hygiene on Monday also issued a statement concerning the patient, saying "after consultation with CDC and Mount Sinai, the Health Department has concluded that the patient is unlikely to have Ebola."

"Specimens are being tested for common causes of illness and to definitively exclude Ebola," the department added.

The man with high fever and gastrointestinal symptoms stepped into the Mount Sinai Hospital's Emergency Department in New York City early Monday morning, and told doctors that he had recently traveled to a west African country where Ebola has been reported, the hospital said.

The patient has been placed in strict isolation and is undergoing medical screenings to determine the cause of his symptoms, according to the hospital.

The Ebola outbreak, which is by far the largest in the 40 years or so history of the disease, has killed some 900 people and affected around 1,600 others this year in four western African countries -- Guinea, Liberia, Nigeria and Sierra Leone, according to the World Health Organization.

Ebola, which spreads through mucous and other body fluid or secretions such as stool, urine, saliva and semen of infected people, can kill up to 90 percent of those who become infected, and the fatality rate in the current epidemic is about 60 percent.

One of the two Americans who contracted the Ebola virus while treating patients in Liberia was brought back to the United States for treatment last Saturday. The second one, missionary Nancy Writebol, is expected to arrive in Atlanta within the next few days.

The U.S. government has issued a warning against nonessential travel to Guinea, Liberia and Sierra Leone, saying it reflects the "worsening" Ebola outbreak in this region.

Border patrol agents at airports in New York and Washington have been told to ask travellers about possible exposure to the virus and to be on the lookout for anyone with fever, headache, achiness, sore throat, diarrhea, vomiting, stomach pain, rash or red eyes.