The London Eye on the South Bank has been closed by a safety scare after it was found to be turning too fast.
Thousands of tourists were left disappointed after the 450ft-high structure was halted because of a computer problem.
A spokesman said up to 10,000 people had tickets for today and were being offered refunds or the chance to ride on another occasion.
"It is basically an IT problem. They were trying to relaunch the software but when they did so the wheel was turning slightly faster than normal," the spokesman said.
"As a precaution we decided to close the London Eye. We are offering passengers either re-bookings or refunds, or obviously they could turn up later on today."
It was hoped to have the Eye working again by 3pm or 4pm this afternoon, the spokesman added.
A letter of apology had been handed out to tourists at the London Eye explaining the situation.
It read: "Since safety is our number one priority, as a precaution we have taken the decision to close the Eye."