The smell of gas is normally the first sign of a gas leak. In this situation check the tightness of your system by turning off the pilot light of your gas appliances and keeping an eye on the gas meter. If the meter is runing very fast, you can locate the leak by closing one by one the safety valves located upstream of the suspected leaking device. When the meter stops spinning, then you have isolated the apparatus or pipe segment responsible for the escape.
If the counter continues to turn when all the taps have been closed (except of course the general upstream of the meter), the loss of gas is on the main pipe, or in the counter itself. If the gas accumulates, the slightest spark can cause an explosion. DO NOT touch light switches and light matches under any circumstances. Immediately stop the flow of gas to the counter and to the various devices. Make sure the rooms are well ventilated, creating a current of air, so as to release the gas out of the house and contained area.
If you hear a whistle sound, then the gas escaping is severe and you can locate it easily by listening to the appliance the sounds coming from. Call a Cairns plumber or gas supplier for repairs straight away.
Do not forget, however to open the windows. Prepare a solution of soapy water with washing up liquid and apply it with your fingers or a brush at the points most likely to be the cause of the problems (valves, fittings etc, ..). Where there is a bubble formation it indicates the presence of the leak.
When you have discovered the source of the leak (or even well before), call a plumber immediately. If the leak comes from a joint, try to tighten the sleeve of the tube with the flat keys or scroll wheel. If the leak continues despite this, call a plumber or your installer.