The superheated fragments left trails across the sky before plunging into the ocean.
Photographer Mark Baker, in Nadi, Fiji, watched the final descent.
"We saw a huge trail of white smoke and about six major pieces of the space station, with a few other little ones, racing across the sky," he said.
"It was unbelievable to see how close it was to us. It must have lasted about 10 seconds and then it passed into the clouds. A couple of seconds later we heard a few sonic booms.
"It was a once in a lifetime experience."
Beach excitement
Another photographer, Rob Griffith, said the lights were blinding. He said: "It was like someone shining a spotlight in your eyes, it was really intense."
He said people watching the spectacle on the beach were gripped by the excitement.
"As it was going across, people were running along the beach following it because they knew it was going to disappear in the clouds," he said.
Flying his light aircraft towards Nadi, Sun Air pilot Neli Vuatalevu had a front-row seat for the fiery disintegration of Mir.
"It was spectacular. The best fireworks I've ever seen. I don't think I'll see anything like it again in my life."
Eye witness Mark Herring, watching from a Fijian beach, said spectators realised the significance of the event.
"People here observed the passing of Mir with a moment of reverence and with respect for the dignity of the historic accomplishment of the Russian space programme," he told BBC Radio 4's Today programme.
There have been no reports of anyone seeing the wreckage actually enter the waters of the Pacific.
Unforgettable
Australian emergency officials who monitored the descent said the debris hit the intended target area to the south-east of Fiji.
Fiji's director of meteorology, Rajenda Prasad, was playing rugby with friends.
"It was very bright - much, much brighter than what we are used to in terms of seeing aircraft flying overhead. It was a spectacular incident and something that we as weather observers will never forget."
A group of Russian and American cosmonauts, scientists, space entrepreneurs, cameramen and fee-paying passengers, set off in two small planes from Fiji to try to record Mir's final moments on film.
But a spokeswoman for the expedition said she had not been able to confirm whether the team got any quality recordings.
Tuna fishing boats in the crash zone have come through the drama undamaged, according to the New Zealand Maritime Safety Authority.
Messages posted on a Californian website by fishermen included one from "Dave" which read: "Missed us. Better luck next time."