UPDATED 4:14pm: A New York doctor has been placed in isolation in hospital after becoming the first confirmed case of the deadly virus in the Big Apple.

Dr Craig Spencer has tested positive after developing a high fever following his return from West Africa where he'd been treating Ebola patients.

It's feared the doctor may have infected others after catching the train, going bowling and riding in a taxi the night before falling ill.

His home has now been sealed off and officials are looking for anyone he might have been in close contact with.

Tests were carried out at New York's Bellevue Hospital after Dr Spencer came down with a fever and stomach problems.

Details of the Dr Spencer's activities in West Africa are yet to be released.

New York officials say the first confirmed case isn't an unexpected circumstance.

New York Governor Andrew Cuomo says the fact the patient is a medical professional himself works in their favour.

"Our best information is that for the relevant period of time he was only exposed to very few people. Partially because he knew exactly what the illness was all about and he was taking precautions on his own."

Mr Cuomo say they are as prepared as they can be for an Ebola case.

"I feel confident that we're doing everything that we should be doing and we have the situation under control."

A team of 'disease detectives' is on the case, and New York's Health Department has specialists tracing everyone he came into contact with.

Dr Spencer's fiancee and two friends are in quarantine, and have shown no signs of being unwell.

Mayor Bill De Blasio says there is no need for New Yorkers to be alarmed.

"We emphasise again - Ebola is very difficult to contract. Being on the same subway car or living near a person with Ebola does not, in itself, put someone at risk."

New York City Health Commissioner Dr Mary Bassett says he left his home a number of times.

He had been for a run, on the subway, out bowling and in a cab before he got sick.

Dr Spencer had also been closely checking his own temperature twice daily, and had been feeling fine before he came down with symptoms of the virus this morning.