A mysterious respiratory illness gripping a central Chinese city has put countries in southeast Asia on high alert after it was feared to have spread to Singapore.

Malaysia, Vietnam and Thailand have begun screening all passengers arriving from the city of Wuhan, where dozens of people have been infected.

In Singapore, a three-year-old girl with pneumonia was warded and isolated as a precautionary measure, after she had travelled there from Wuhan.

But on Saturday, the Ministry of Health said tests confirmed her pneumonia was not linked to the virus outbreak, reported local news site Today Online.

“Epidemiological investigations, clinical assessment and laboratory results … showed the case is not linked to the pneumonia cluster in Wuhan,” said the ministry.

Mysterious mist engulfs Chinese city of Wuhan Show all 3 1 /3 Mysterious mist engulfs Chinese city of Wuhan Mysterious mist engulfs Chinese city of Wuhan 1.jpg A busy intersection in Wuhan on June 11 Getty Mysterious mist engulfs Chinese city of Wuhan Untitled-1.jpg A woman wears a mask as she walks along a street in front of a Chinese temple during a hazy day in Wuhan, Hubei province June 11. Getty Mysterious mist engulfs Chinese city of Wuhan Untitled-2.jpg Chinese motorists wear masks as they make their way along a busy intersection in Wuhan on June 11 Getty

Health authorities in Malaysia have set up testing facilities in airports to single out any passengers with abnormal temperatures.

“We will monitor the international entry points to ensure that arrivals from Wuhan go through temperature screening, and if [a] temperature is detected, a second examination will be carried out at the quarantine centre.

“Those suspected of being infected by the illness would be referred to the nearest medical facility,” said the Malaysian Health Ministry’s Disease Control Division.

In Thailand, public health minister Anutin Charnvirakul urged the general public to stay calm and said airports serving daily flights from Wuhan have also had temperature screening devices installed.

According to the Bangkok Post, Mr Charnvirakul said health officials have dealt with communicable diseases including bird flu and SARS before.

He said: “We have things under control. There’s no problem here.”

Hong Kong authorities have activated a newly created “serious response” level in response to the outbreak.

The Hospital Authority there said on Sunday there were 15 patients being treated for symptoms after recent visits to Wuhan.

As of Sunday, 59 people were diagnosed with the mystery illness, which has been dubbed Wuhan pneumonia, and have been isolated while they receive treatment.

The Wuhan Municipal Health Commission said seven of those diagnosed were in critical condition.

Initial investigations ruled out SARS as well as Middle East respiratory syndrome, influenza, bird flu and adenovirus.

“As of now, preliminary investigations have shown no clear evidence of human-to-human transmission and no medical staff infections,” said the commission.

The spread of the illness in the city echoes the 2002-03 severe acute respiratory syndrome (SARS) epidemic that killed more than 700 people in mainland China, Hong Kong and elsewhere.

Several patients were working at the South China Seafood City food market in Wuhan, which the World Health Organisation (WHO) said could indicate an exposure link to animals.