Public Health England is advising pregnant women to consider postponing non-essential travel to Florida because of the Zika virus.

It comes after health officials in the US discovered four cases of the virus, which it is feared were contracted from mosquitoes inside America and are not linked to foreign travel.

PHE said the risk in Florida is moderate, while in many countries in South America, including Olympics host Brazil, it remains high.

Its updated advice says: "Pregnant women should consider postponing non-essential travel to affected areas until after the pregnancy."

Image: Zika has been linked with the birth defect microcephaly

However, it adds that the current "active transmission" area is small and confined to a one square mile area of Miami-Dade County.

Zika has been associated with the birth defect microcephaly, which can cause children to be born with abnormally small heads and brain damage.

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America's Centers for Disease Control and Prevention (CDC) has said the four Florida cases found so far were probably caused by bites from local Aedes aegypti mosquitoes.

Its director, Tom Frieden, said: "All the evidence we have seen indicates that this is mosquito-borne transmission that occurred several weeks ago."

The White House said the cases should be a "wake-up call".

President Obama has asked his team to ensure Florida has the support it needs after being briefed on the new cases.

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More than 1,650 Zika infections have been reported across the US.

Meanwhile, three more people have been found to have Zika in the UK after returning from overseas.

The cases were discovered by the Calderdale and Huddersfield NHS Trust in West Yorkshire between April and June.

The trust's infection control lead, Dr Gavin Boyd said: "There is extremely low risk of contracting Zika virus in the UK as the mosquito that transmits the virus is not present in the UK.

"There is no specific treatment and it wears off naturally after two to seven days.

"After a diagnosis patients are cared for by their GPs."

The number of people treated for Zika in the UK has now reached 53.

Almost 5,000 cases of microcephaly have been recorded in regions affected by Zika since the epidemic began last year.

Northeastern Brazil has been the main area of concern, but more than 20 other countries have now been affected by the virus.