The airport in Australia's capital city of Canberra has been shut down due to the threat of approaching bushfires.Flights were cancelled out of Canberra Airport, a 20 minute drive from Parliament House in the city centre.A heatwave sweeping the nation's south-east caused existing blazes to flare up again on Thursday, officials said.There are reports that a fire-fighting aircraft has crashed in the Snowy Mountains, two hours south of the capital.The New South Wales (NSW) Rural Fire Service said it had lost contact with one of its large air tankers on Thursday afternoon.There are more than 100 blazes raging across the state of NSW as hot and windy conditions return to the region.In Canberra, officials issued emergency warnings urging people to stay away from the airport as two blazes threatened to breach the airfield perimeters.Authorities said the blazes threatening Canberra Airport had escalated after first appearing on Wednesday.The capital, located in an administrative region between Sydney and Melbourne, has had large blazes raging on its outskirts for weeks.Smoke from the fires has caused severe air pollution problems, with the city suffering the worst air quality in the world for several days earlier this year.

Fire threat returns

Since September, Australia has battled an ongoing bushfire crisis which has killed at least 30 people.More than 10 million hectares - an area almost the size of England - have been destroyed in blazes which have had the most impact in NSW and Victoria states.Recent days of thunderstorms and rain across fire grounds had helped halve the number of blazes burning in the region since the start of the year.However, fire chiefs warned that the sporadic rain would only provide short-term relief ahead of the return of dangerous conditions. Smoke from the fires shrouding Parliament House in Canberra on ThursdayTemperatures in Sydney on Thursday soared past 40C (104F) in the city's west."We've got thousands of kilometres of fire perimeter," NSW Rural Fire Services Commissioner Shane Fitzsimmons told reporters on Thursday."All of the fires that we've still got, whether they're under control or are still being worked on, are going to be tested today."By midday on Thursday, more than half a dozen blazes were burning at "emergency level" on the south coast. Severe thunderstorms and hail caused havoc in Canberra and Melbourne earlier this week