Aid organisations need money, not food or clothing, to help Samoans and Tongans in the wake of a devastating tsunami.

The Australian Red Cross estimates 15,000 people have been affected by the disaster in Samoa alone, while 1,000 are living in relief camps.

It's sending three specialised aid workers to help more than 100 Samoan-based volunteers register people at evacuation centres, provide basic first aid and assess the impact of the disaster on local communities.

Australian Red Cross international emergencies manager Carmel Flynn said the Australians would touch down in Samoa on Friday, one an expert in psycho-social support, another in water and sanitation and a third to help restore contact between families dispersed as a result of the tragedy.

The organisation has also launched an appeal for cash donations, which Ms Flynn hoped would be enough to provide long-term aid to Samoa while it rebuilds.

"Money will go towards the immediate response, the provision of relief items such as food, water and emergency shelter," she told AAP on Thursday.

"If we raise enough, it will also help in terms of the recovery of those communities."

Donations of goods won't be accepted because it's more helpful to source these things in-country.

"That helps local businesses get back on top of their own livelihoods," Ms Flynn said.

"It also ensures the most appropriate kind of goods are provided to the communities that have been affected."

Catholic aid agency Caritas Australia is another group responding to the plight of Pacific Island tsunami victims.

Chief executive Jack de Groot said the organisation's Samoa branch had been actively involved in the clean-up but needed help distributing food, shelter and psycho-social programs.

He said Caritas Australia would send a staff member within the next day and had launched its own appeal to fund the recovery.

"In this sort of tsunami, people lose everything," Mr de Groot said.

"We're looking towards rebuilding houses, rebuilding livelihoods ... (providing) the real basics of food, clothing, water and still making sure that those requiring medical assistance have got access to it."

Meanwhile, immunisation supplies, oral rehydration salts and water purification tablets have been sent by UNICEF's Pacific office to Samoa and Tonga.

The organisation is also going to set up nutrition and water and sanitation programs, as well as child protection measures for the 6,000 young Samoans impacted by the disaster.

"This is a tragedy of unbelievable proportions," UNICEF spokesman Dr Isiye Ndombi said.

"UNICEF is ready to work closely and in coordination with our Samoan and Tongan partners and international agencies to provide immediate relief and support."

A massive quake struck Samoa and American Samoa early on Tuesday morning local time (Wednesday AEST), triggering a tsunami that raced across the Pacific.

The death toll from the disaster is expected to climb into the hundreds.