Thousands of twins packed two-by-two into a stadium in Sri Lanka's capital on Monday - so many that officials struggled to count them in time to prove they had organised a record-breaking gathering.
Huge queues built up at the open-air venue in Colombo as sets of siblings waited to get their birth certificates checked. Many appeared to leave before they could be added to the tally.
The last record was set in Taiwan in 1999, when 3,961 sets of twins, 37 sets of triplets and four sets of quadruplets gathered outside Taipei City Hall.
"The counting is still going on. We will submit the final count and the documentation back to the Guinness World Record committee and I am confident we will be informed in writing that we hold the record," Upuli Gamage, co-organizer of the event with her twin Chamali, told the crowd.
There was no immediate comment from the Guinness organisation on whether the event had met the requirements to claim the record.
Many of the twins - including children, pensioners and police officers - had travelled for hours to attend the event, which had Sri Lanka's prime minister, Mahinda Rajapaksa, as guest of honour.
"It's fascinating," said Raheen Usman, a 19-year-old from Colombo, there with her twin Farheen.
"I have made a lot of new friends - all of my friends are twins now."
The record-breaking attempt was followed by a concert performed exclusively by twins, including an 80-member orchestra.
The campaign group Sri Lanka Twins said it had organised the event to raise the profile of underprivileged twins, triplets and quadruplets. Poorer families often struggled to cope with multiple births, it added.