Chch-Melbourne flight forced to turned back twice

A Qantas flight destined for Melbourne has departed from - and returned to - Christchurch twice today, in what the airline says are unrelated events.

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

A Qantas spokesperson says 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 again turned back to Christchurch, this time due to an unusual smell in the cabin.

The spokesperson says the two incidents are unrelated.