NEW YORK (Reuters) - Two travelers who returned recently from separate West Africa trips tested negative for Ebola on Thursday at hospitals in New York and Missouri and will stay under observation while awaiting additional confirmation of the results, health officials said.

Preliminary test results showed a traveler who returned to the United States from a trip to Mali does not have the disease, but the patient remains in isolation at Bellevue Hospital Center for further testing, the New York City Health and Hospitals Corporation said in a statement.

Initial tests for the Ebola virus were negative as well in Crystal City, Missouri, for a patient who recently returned from West Africa, Mercy Jefferson Hospital said.

That patient was being held in isolation at an off-site surgical center and was considered at low risk for Ebola, the hospital said. She will stay in isolation as a precaution and will be retested Saturday night if she remains symptomatic.

Mercy said it was also testing for malaria, the flu and other possible diseases or illnesses. It was withholding further information about the patient, but local media described her as a nurse. Hospital officials did not disclose what country the patient visited in West Africa.

Mali shares a border with Guinea, one of three West African nations hardest hit by the virus. The worst outbreak of Ebola on record has killed at least 5,420 people out of at least 15,145 cases reported since March, mostly in Guinea, Liberia and Sierra Leone. Six people in Mali have died so far from Ebola, according to the World Health Organization.

The New York City health department has designated Bellevue, the country's oldest public hospital, as the facility where any suspected Ebola patients in New York would be transferred.

Last week, the hospital discharged a New York doctor cured of Ebola, which he contracted treating patients in Guinea while working with the humanitarian group Doctors Without Borders.

(Reporting by Barbara Goldberg in New York; Additional reporting by Brendan O'Brien in Milwaukee; Editing by Sandra Maler, Mohammad Zargham and Alan Crosby)