Australia and New Zealand are to airlift equipment to the Pacific nation of Tuvalu to help it deal with a severe water shortage caused by drought.
Military planes from both countries will fly a large desalination unit to Tuvalu's main island of Funafuti.
New Zealand has already flown smaller units to Tuvalu but its foreign minister said more capacity was needed.
Tuvalu has declared a state of emergency over the shortage, caused by the La Nina weather phenomenon.
It has not rained in the remote nation of about 11,000 people for more than six months, and there is no drinkable groundwater because rising seas have contaminated it.
About half the population live on the main island of Funafuti, where water is being rationed.
"The advice is that more capacity is needed to relieve the acute water shortage and replenish stocks," New Zealand Foreign Minister Murray McCully said.
"At present the two operating desalination plants at Funafuti are producing a combined volume of 43,000 litres a day. The minimum requirement for the 5,300 residents is 79,500 litres a day."
Several New Zealand military aircraft and an Australian C-17 - a large military transport aircraft - will be involved in the operation, Mr McCully said in a statement.
The first flight was due to leave on Friday, with the desalination plant due to be moved via Samoa early next week.
Australia has also sent 1,000 rehydration packs for hospitals in Tuvalu, and has provided money and fuel to keep desalination plants going.
Earlier this week, the Tuvalu Red Cross warned that water supplies in some areas - including outlying islands - could run out within days.
Neighbouring Tokelau has also declared a state of emergency over a water shortage. A US coast guard vessel is on its way to the tiny three-atoll territory with 36,000 gallons of fresh water.
It will meet a New Zealand team carrying equipment in Samoa and then proceed to Tokelau.
US Ambassador to New Zealand and Samoa David Huebner said a quick response was needed.
"We are talking about approximately 1,500 people who could be out of fresh water within a week, so we really needed to act very quickly."