Air New Zealand and Qantas are among several airlines that have cancelled flights to and from Bali due to volcanic ash blanketing flight paths.
Mount Lewotobi's Laki-laki volcano in Indonesia erupted on November 3, killing at least 10 people.
It erupted shortly before midnight (local) time, sending lava and rocks flying, with some hitting villages 4km from the crater, burning homes.
The Indonesian Center for Volcanology and Geological Disaster Mitigation (PVMG) said at the time it was clearing a 7km around the eruption, displacing thousands of people.
Since the initial event, the volcano has erupted repeatedly. It is now spewing ash 8000m into the air, which has become a problem for airlines.
Air New Zealand said volcanic ash conditions on the flight path from Auckland to Denpasar in Bali caused the cancellation of flights NZ62 and NZ63 yesterday.
"The safety of our people and our customers is our utmost priority, and we will continue to monitor the movement of the ash over the coming days and its impact to operation of our flights," chief operating officer Alex Marren said.
Customers would be re-accommodated on the next available Air New Zealand service.
Qantas was urging customers to reconsider all non-essential travel to Denpasar up to November 22, saying it had additional flexibility for those who no longer wished to travel.
On its website, it said the "additional flexibility" included fee-free refunds, travel credit or a date change.
The Australian airline confirmed it cancelled flights to and from Denpasar on Tuesday and yesterday.
In a statement, it said its meteorology team was closely monitoring the situation and customers would be contacted directly if their Thursday service was affected by 12pm (NZ time).
Qantas said it was continuing to regularly update customers via its website.
Bookings for flights to and from Denpasar were unavailable until November 18 to allow the airline to accommodate existing bookings, it said.
