A new type of virus originating from a city in central China may have infected far more people than first thought.Two people in Wuhan have died after an outbreak of pneumonia linked to the new strain which is believed to have come from a seafood market.On Saturday, health officials in the city confirmed four more people had contracted the illness.

Differing reports now place the total number of infections at 45 or 50 cases.But a study from London's Imperial College suggests there could be more than 1,723 cases in Wuhan alone.It said: "It is likely that the Wuhan outbreak of a novel coronavirus has caused substantially more cases of moderate or severe respiratory illness than currently reported."Image:A notice for passengers from Wuhan, China is displayed near a quarantine station at Narita airport in JapanDoctors began seeing people with symptons including fever, cough and breathing difficulties, in people who worked at or visited the market late last month.Local health authorities and the World Health Organisation (WHO) have not concluded that the virus can be passed from person to person.

Officials currently believe it is spread from animals to people.But the new report suggests they could be wrong.

"Self-sustaining human-to-human transmission should not be ruled out," it says.Image:A security guard outside the closed Huanan Seafood Wholesale MarketThere are also concerns that the disease could spread across China and internationally.400 million Chinese people are expected to make 3 billion trips as they travel to celebrate the lunar new year around 24 January.Two cases have been reported in Thailand and one in Japan.

All three victims had recently been in Wuhan.Image:A woman wears a mask near the closed Huanan Seafood Wholesale MarketThe United States and most Asian countries have stepped up screenings of people travelling from Wuhan and the WHO has warned hospitals worldwide that a wider outbreak is possible.Passengers arriving at Los Angeles, San Francisco and JFK airport in New York City will have their temperatures taken and be asked about symptoms.Authorities are keen to avoid a repeat of the SARS (severe acute respiratory syndrome) outbreak in 2002 and 2003, which also originated in China.

SARS killed 800 people worldwide.Image:Medical staff transfer patients to Jin Yintan hospital in WuhanTemperature tests started at Wuhan's Tianhe international airport on Wednesday but two flight attendants who were working at domestic terminals told Reuters they had not received any extra training or warnings.Hospital authorities and police have warned people against speaking about the virus online or to the media, with eight people "dealt with" earlier this month after sharing information online.