Chch-Melbourne flight forced to turn back twice

A Qantas flight destined for Melbourne departed from - and returned to - Christchurch twice on Monday in what the airline says were unrelated events.

The Boeing 737-838 first took off from the Garden City about 6.45am before turning around over the Tasman Sea and returning to Christchurch Airport.

A Qantas spokesperson says the pilots chose to return due to an issue with their radio, which was fixed by engineers before taking off again for Melbourne.

But following a second departure around 9.40am, the plane was again forced to turn back to Christchurch, this time due to an unusual smell in the cabin.

The spokesperson says the two incidents are unrelated.