The Australian government has cited Hong Kong's air pollution as a potential health issue, in a new travel warning to its citizens. Australia's Department of Foreign Affairs issued the updated travel advice on Monday, which is sent to all subscribers and posted on its Smartraveller website. It comes amid the ongoing debate over how air pollution in the city should be monitored and whether World Health Organisation- approved targets for pollutants should be adopted. The travel advice highlighted air pollution levels when Australians travelled to the city. 'The levels of air pollution in Hong Kong may aggravate bronchial, sinus or asthma conditions,' it said. 'People with existing heart or respiratory illnesses should reduce physical exertion and outdoor activities on days when very high pollution levels are recorded.' It advised visitors to check pollution levels on Hong Kong's Environmental Protection Department website. The Smartraveller website also highlighted pollution levels on the mainland, particularly those in the industrialised areas of Beijing, Shanghai and Guangzhou. Although the site suggests the bad air may 'aggravate bronchial, sinus or asthma conditions', it does not offer advice to travellers to avoid activity. Air-quality concerns regarding seasonal haze in Singapore and Thailand are also included. A spokesman for the Australian department said the travel advice was changed during quarterly updating. Last night he could not say why air pollution was now included, when it had previously not been. Clear The Air chairman Christian Masset said the warning made it clear that Hong Kong's air quality was no longer just a local issue. He said the warning could shame the city into acting faster to reduce fine particles known as PM2.5 and to phase out diesel engines, which he said would be 'a good thing'. He said tourists should be warned about pollution as it was 'a fact'. 'They should be warned they might not see the harbour from The Peak. The tourists who have been fortunate enough to come when the wind was blowing the right way have nothing to complain about, but for others it might make them think twice about coming to Hong Kong. 'It is a major deterrent to developing a sound tourism industry.' A spokesman for the Environmental Protection Department said pollution levels varied and normally did not affect residents' and visitors' daily activities. Asked if visitors should be concerned, he said the government had taken measures to improve air quality, but added: 'Hong Kong, like most metropolises in the world, has a heavy concentration of people and activities that could strain its air.' He said roadside levels of respirable particulates, nitrogen oxides and sulfur dioxide had fallen by 21 per cent, 23 per cent and 19 per cent respectively since 1999. The 2008 Lonely Planet travel guide said air pollution was 'perhaps Hong Kong's most pressing environmental problem', causing up to 15,600 premature deaths each year. Yesterday's air pollution index was medium to high, with the Mong Kok roadside station recording the highest reading of 73.