A second New Zealand health worker has been isolated as Ebola tests are carried out after returning from the international mission to fight the deadly virus in West Africa, Health Minister Jonathan Coleman said Thursday.

"The patient has recently been in Sierra Leone as part of New Zealand's contribution to the international response to Ebola," Coleman said in a statement.

The unidentified patient had left Sierra Leone on April 15 and had reported "minor symptoms" to a public health officer on Wednesday.

The patient was being cared for in a special isolation facilities in Wellington Hospital, while blood samples were sent to Australia for testing, which could take 24 to 48 hours.

"The only person who has been in contact with the patient during the potentially infectious period has been the patient's partner. The partner is being monitored according to international protocols," said Coleman.

Another New Zealand health worker was isolated last month after falling ill on her return from West Africa, but Ebola was later ruled out as the cause of the illness.

Ebola transmission required direct contact with an infected individual and only occurred through contact with blood and other body fluids.

People with Ebola were not infectious until they displayed symptoms, said Coleman.

If the healthcare worker did have Ebola, they would not have been infectious while traveling as the individual was not symptomatic at that time.