A cloud of ash from an erupting volcano in Chile has drifted higher over New Zealand and Australia, easing the threat to commercial aircraft.

Scores of flights had been cancelled over the past two days, grounding thousands of travellers.

Australia's national carrier, Qantas, resumed flights in and out of the southern city of Melbourne, but is still not flying to or from New Zealand or within the country.

Flights between the two countries and some domestic routes in both had been affected by the cloud, which has travelled some 10,000km across the Atlantic and Indian oceans, settling over their southern air space.

New Zealand's Civil Aviation Authority said the cloud had moved higher with the base at around 27,000 feet (8,200m) from the previous 20,000-foot level.

Air New Zealand kept in the air by rerouting flights and flying at lower altitudes to avoid the ash, but was monitoring developments closely.

Air NZ flights had been operating at around 18,000 feet although it meant fuel consumption was up around 10%.

Virgin Australia, which had cancelled services yesterday, resumed flights today.

The volcano in the Puyehue-Cordon Caulle chain in Chile has been erupting for the past week, throwing South American air travel into chaos as it spews ash high into the atmosphere.

Meanwhile, UN Secretary-General Ban Ki-moon was forced to rough it on an overnight bus to meet Argentine leaders because of the ash cloud. Worse still - it was his birthday.

Mr Ban did not have time to change his arrangements after his flight was diverted to Cordoba and he had to slog it 700km overnight to Buenos Aires in a bus.

'He and his delegation went to the capital by bus through the night,' said UN spokesman Martin Nesirky.