Qantas and Jetstar have lifted a ban on flights to and from Melbourne but services by the two airlines in and out of the southern island of Tasmania and New Zealand remain grounded.

Flights to Adelaide by Qantas, Jetstar and Tiger were also grounded Tuesday with a review on the situation later expected in the day.

"Qantas will continue to monitor the movement of the ash cloud and assess its impact on flight operations as the situation develops," the airline said in a statement.

"The Qantas Group's approach to flying is based on the highest standards of safety and risk assessment. Safety is always put before schedule."

While Qantas continues to take a conservative approach, Virgin has resumed normal flights to Melbourne, Tasmania and New Zealand with its planes flying around or under the ash plume.

They are also flying in and out of Adelaide, as are international services by Singapore Airlines and Malaysia Airlines.

"Additional flights will be implemented between Sydney and Melbourne and Melbourne and Hobart to carry impacted guests,' Virgin said.

Air New Zealand's domestic and trans-Tasman flights continue to operate to schedule.

"By adjusting cruising altitudes of our aircraft we are able to continue to safely deliver customers to their destinations," Air New Zealand said.

Strong winds have carried the ash more than half way around the world, over the southern Atlantic and southern Indian Oceans to Australia and as far as New Zealand since Chile's Puyehue volcano erupted over a week ago.

Andrew Tupper, the Australian Bureau of Meteorology's Volcanic Ash Advisory Centre head, warned the crisis was not yet over.

"I think it's fair to say there will be more disruption, so that's the bit of bad news," he told ABC radio, adding that while the ash was heading back to South America, it could return to Australia.

"It has been known to do a double lap in the past," he said.

The flight disruptions have affected an estimated 60,000 travellers.

The eruption of the Dubbi volcano sent a plume of ash up to 15 kilometres into the air, the Volcanic Ash Advisory Centre said, disrupting air traffic in Eritrea and neighbouring Ethiopia, and threatening further disruptions in the region.

German airline Lufthansa said it had cancelled two flights to the region and a senior US official said Clinton was leaving the Ethiopian capital Addis Ababa for fears of being stuck there by the ash cloud.

The official said Clinton and her delegation were leaving "because the ash cloud is moving towards Addis and it could cover the city... for an indeterminate length (of time)."

An AFP reporter confirmed her plane had departed at about 10:00 pm local time (1900 GMT).

Clinton was supposed to have stayed in Ethiopia until Tuesday afternoon as part of a tour of African nations.

The eruption, which began at 2100 GMT on Sunday and was continuing late Monday, was "significant" according to Jean Nicolau of French weather service Meteo-France, which houses the VAAC's operations for southern Europe and Africa.

"Based on satellite images we are seeing, the volcanic ash is reaching altitudes of 13 to 15 kilometres" (42,650 to 49,200 feet), he said, adding: "We are not in a critical situation like with the Icelandic volcano Grimsvotn, which concerned a very busy air traffic zone, because the traffic is much less important" in east Africa.

The eruption was the volcano's first since 1861.

According to preliminary Meteo-France simulations, the lower-density ash clouds were heading west/northwest toward Sudan, while the higher-density clouds were heading west/southwest.

"If the cloud reaches Egypt, Israel or the Arab peninsula, the impact on air traffic will be more significant, but it is too early to know," Nicolau said.

In Berlin, Lufthansa spokesman Marco Dall'Asta said the company's Frankfurt- Addis Ababa flight had been cancelled and that its flight from Frankfurt to the Eritrean capital Asmara via Jeddah had been stopped in Jeddah.

"Nothing has yet been decided for tomorrow (Tuesday)," he said.