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The warnings travelled quickly across the Pacific in the middle of the night: an 8.9-magnitude earthquake in Japan had spawned a deadly tsunami, and it was racing east as fast as a jetliner.
Sirens blared in Hawaii. Californians pulled back from the shoreline, fearing the worst. Pacific Islanders fled to the hills, and South American cities were evacuated.
Fishermen took their boats out to sea and safety.
The alerts moved faster than the waves, giving millions of people around the Pacific Rim hours to prepare.
None of the damage - on the Pacific's hundreds of atolls, in the US, South America or Canada - was anything like the devastation in Japan.
The warnings and the response showed how far the earthquake-prone Pacific Rim had come since a deadly tsunami caught much of Asia by surprise in 2004.
"That was a different era," said Gerard Fryer, a geophysicist with the Pacific Tsunami Warning Centre.
"We got the warning out very quickly. It would not have been possible to do it that fast in 2004."
No more than 10 minutes after Japan was shaken by its biggest earthquake in recorded history the centre had issued its warning. As the tsunami raced across the Pacific at 800km/h the first sirens began sounding across Hawaii.
Amateur video footage showed Hawaiians skipping on the seawall as the waters washed around them and up into the lobbies of expensive hotels.
In Tonga, thousands of people in the capital Nuku'alofa sought refuge at the King's large residence on higher ground. But worse was to come for them: early in the afternoon, the kingdom of 176 islands was struck by its own big earthquake, with a magnitude of 6.1.
Harbours and marinas in California and Oregon bore the brunt of the damage on the Pacific Rim, estimated by authorities to be in the millions of dollars.
Boats crashed into each other, some vessels were pulled out to sea and docks were ripped out. Rescue crews searched for hours for a man who was swept out to sea while taking pictures.
Heavy swells rolled through the port and marinas of Mexico's Baja California resort of Cabo San Lucas, rocking boats at anchor, but they did not bring any reports of damage.
Mexican officials closed the cargo port of Manzanillo and officials said some cargo ships and a cruise liner had decided to delay entering port to avoid possible problems from any rough water.
Only slightly higher waters than normal came ashore on the coasts of Honduras and Colombia, Ecuador's Galapagos Islands, and then the mainland in Peru and Chile.
Some of the strongest action was taken by Ecuadorean President Rafael Correa, who declared a state of emergency, closed schools, and ordered people on the Galapagos Islands and the coast of the mainland to seek higher ground.
On Chile's Easter Island, in the remote southeast Pacific, residents and tourists evacuated the only town, Hanga Roa, which faces Japan.
Left behind were the famous moai head sculptures, carved from volcanic rock by the islanders' Rapa Nui ancestors, looking silently out to the ocean that, once again, was Pacific.