Two young patients have been tested at a hospital in Newcastle for Ebola.
The children had shown viral symptoms and spent time in Africa. They are also undergoing tests for malaria.
Public Health England, which admitted it was uncertain where in Africa they came from and when they arrived in the UK, said it was "unlikely" they had Ebola.
The children had tests for the deadly virus on Thursday afternoon and the results are expected later on Friday.
They are in the Infectious Diseases Isolation Unit at the Royal Victoria Infirmary, one of three units outside London geared up to care for patients with infectious diseases such as Ebola.
A spokesperson for Public Health England in the North East said: "Due to uncertainty about where in Africa the children are from and when they arrived in the UK, as a precaution the children are being tested for Ebola and malaria.
"However, the clinical and Public Health England risk assessment is that Ebola is unlikely.
"People who have been in contact with the children have been advised to continue as normal."