The crane, which was working inside the structure, pierced the inner and outer panels of the roof, exposing the interior.
The damage was temporarily repaired. But a dome insider said replacement panels would have to be shipped from the USA.
A spokesman for the New Millennium Experience Company confirmed that the roof had been torn, but insisted that the damage was slight.
“A crane put a very small tear in the roof. We patched it and will replace the damaged panel in due course. It’s the equivalent of replacing a tile on your roof.” The spokesman confirmed that new panels had to be ordered from the fabric manufacturer in the USA, but was unable to put a cost on the repair.
The spokesman added that the accident would not delay the dome’s opening and that work on the controversial £800m project was on schedule.