Eamonn Glover described how, in May 2000, he saved himself by clinging to a hand rail on the tower block he was working on as the crane came away from its fixtures.
The jury at St Pancras coroner's court was told that the men who died, Peter Clark, 33, Martin Burgess, 31, and Michael Whittard, 39, were part of a six-man team. They were using a climbing frame to extend the height of the crane, known as TC-3, at the HSBC site in Docklands when the accident happened. They were employed by Hewden Tower Cranes of Castleford, West Yorkshire.
Glover told the court that he had seen the climbing frame twisting around the newly inserted section of the crane. He said that his mind went momentarily blank, and that when he opened his eyes the top of the crane and the frame were lifting off above him. He said: "Everything came over the top of my head."
Gareth Hetherington, who had been with Glover, said he had seen the metal of the climbing frame bowing slightly when the team inserted the previous section.
Hetherington said that as the engine started to lower the final section into place he heard a popping, banging sound and the whole crane shook violently as the top section became detached. He told the court: "I thought the whole thing was coming down."
Hetherington told the court that the team worked 80-100 hours, seven-days a week, and had been on site since 6.30 that morning, but were still slightly behind schedule.
He said the team had been due to knock off in about 15 minutes, at about 4.15 pm, when the accident occurred. All they had to do was to insert the final section of the extension and they would have been finished for the day.
The court heard that the crane had no anemometer to measure wind speed and no plug fitted to the electromagnetic break to prevent the jib from slewing while sections were put in place. However, the court was told that this was not unusual.
Paul Plumpton, who was operating crane TC-2 at the site, said it was standard procedure to switch off the engine from the cab, so there was no power to move the jib in any direction while the hydraulic ram was being used.
The court heard the workers who operated the cranes were certified to do so, but most of the crew had no formal training.
The case is due to finish today.