The Bureau of Meteorology (BOM) says that Aussies should expect their Christmas travel plans to be disrupted by a Christmas heatwave that brings hot air for seven consecutive days.

According to BOM Western Australia is already experiencing a heatwave and the hot air coming from the region is starting to spread across the country.

Regions in South Australia and western Victoria, New South Wales, Queensland and the Northern Territory are likely to experience 40 degrees from Friday, Dec 20.

"Unfortunately it is going to be a fairly protracted period of hot weather. Maybe in some of the coastal locations it won't be quite so protracted, but over inland parts of south-eastern and eastern Australia. I think we are looking at around about a week's worth of very hot weather. This is the first protracted heatwave of the spring-summer period over such a large area. People should be aware that it is going to get very hot. Travel plans [may] start to be disrupted. We are starting to see some potential cancellations of train services in some areas due to expected buckling of lines. It's not that unusual at this time of year, the sun is almost exactly overhead at the present time. But for a period of a week or so then, to see these kinds of temperatures repeated day after day is a little unusual. It's highly likely that we will see a lot of that heat remain over central Australia. Possibly into the early part of the new year we are likely to see a return to some very hot conditions," BOM's assistant director of weather services, Alasdair Hainsworth explained.

BOM added that the heatwave may continue to hit the country up until the early parts of January 2014.

BOM said that hot weather conditions in 2013 continue to be much warmer than any previous calendar year. In fact, 2013 will likely be Australia's hottest year on record. BOM will issue a complete summary of the Climate of 2013 on Jan 3, 2014, in the Australian Annual Climate Statement.