The Pacific Tsunami Warning Center recorded a 3-inch (76 mm) rise in sea levels near the epicenter, and New Zealand scientists determined that the waves measured 14 metres (46 ft) at their highest on the Samoan coast.

This is part of the Pacific Ring of Fire, where tectonic plates in the Earth's lithosphere meet and earthquakes and volcanic activity are common.

[11] American Samoa Governor Togiola Tulafono was in Honolulu, Hawaii for an ocean policy conference at the time of the tsunami struck.

"[13] Tulafono departed Hawaii for American Samoa on a United States Coast Guard supply flight from Honolulu on the evening of 29 September.

Lieutenant Governor Ipulasi Aitofele Sunia announced that the earthquake had caused severe damage to American Samoa's electrical infrastructure.

[12] U.S. President Barack Obama declared a major disaster in American Samoa, allowing federal funds to be used for rescues, life support, and public health and safety measures.

Also, basic needs and basic commodities, including electrical generators, medical supplies, and pharmaceutical drugs were sent out, and multiple planes are being prepared for more cargo and personnel, including FEMA, HHS, and Coast Guard staff and experts from the Environmental Protection Agency, U.S. Army Corps of Engineers, and Red Cross.

[18] Journalist Cherelle Jackson reported that the city quickly emptied in the aftermath of the earthquake and tsunami, "All the schools, workplaces everyone has walked up – it's like a ghost town.

"[18] Twenty villages on Upolu south side were reportedly destroyed, including Lepā, the home of Samoa's Prime Minister[19] Tuila'epa Sa'ilele Malielegaoi.

New Zealand Prime Minister John Key arrived in Samoa on 3 October and visited some of the most damaged areas on Upolu including the villages of Poutasi and Lalolamu.

[46] Tonga's acting Prime Minister Lord Tuita said the government is sending a second plane to Niuatoputapu, but that communication links have been damaged.

[46] Relief efforts undertaken by the Tongan government and Red Cross focused on Niuatoputapu, with support from Australia, New Zealand and France.

[47] French High Commissioner Adolphe Colrat warned residents of the Marquesas to seek shelter at an elevation of at least 10 m (33 ft) above sea level.

Residents across French Polynesia were advised to avoid valleys and bays, tie up watercraft and listen to Réseau France Outre-mer (RFO) for further instruction.

[47] Five small tsunami waves, measuring 25–70 cm (10–28 in) were recorded off the coast of Papeete, Tahiti, between 11:10 am and 12 noon local time on Tuesday.

[47] The Colombian Navy training ship Gloria, also left Papeete Harbor in Tahiti once the warning was issued as a precaution.

[47] Residents of the Society Islands, which include the tourist resort areas of Tahiti and Moorea, were advised to move above 5 m (16 ft) above sea level, for safety.

[47] High Commissioner Adolphe Colrat cancelled the tsunami red alert at 12:03 pm on Tuesday for all areas of French Polynesia except the Marquesas.

[47] French Polynesian President Oscar Temaru wrote to the heads of American Samoa, Samoa and Tonga offering support following the tsunami,[48] "On behalf of the people and the government of French Polynesia, I would like to convey our most sincere expression of condolence and solidarity in the wake of the Tsunami that just hit your people...We have, within the FRANZ framework decided to send both human and material help.

"[48] FRANZ stands for France, Australia and New Zealand, three large countries who traditionally provide aid in Oceania following natural disasters.

A further 7 RNZAF and 2 Royal Australian Air Force Hercules flights were made, and a RAAF C-17 Globemaster also provided airlift support to ferry relief supplies.

[51] Air New Zealand arranged for larger Boeing 777 aircraft to carry in relief workers and evacuate tourists to Auckland, and fly the Samoan Prime Minister back to his country.

[55] The United States sent the US Navy frigate USS Ingraham, two US Air Force C-17 Globemaster III aircraft from the 154th Wing, and 90 members of the Hawaii National Guard to American Samoa to assist in the relief efforts there.

[71] A tsunami warning remained in effect for the Marquesas Islands of French Polynesia, as five main waves were expected to strike that archipelago.

A tsunami watch was issued for islands farther from the epicenter, including Hawaii and Papua New Guinea, but not for California, USA.

[73] A tsunami advisory was issued for coastal California and the San Francisco Bay Area beginning at 9:00 pm local time as a precaution.