At least some customers of Coinbase's U.S. cryptocurrency exchange are showing $0 account balances Wednesday as bitcoin (BTC) posted – and then quickly erased – a gigantic rally.

The exchange said on its website that it was investigating the matter.

"We are aware that some users may see a zero balance across their Coinbase accounts and may experience errors in buying or selling," Coinbase said. "Our team is investigating this issue and will provide an update shortly. Your assets are safe."

Coinbase CEO Brian Armstrong later said that the exchange had modeled a 10 times surge in traffic but that Wednesday’s demand exceeded that number.

“It’s expensive to keep services over-provisioned, but we’ll need to keep working on auto-scaling solutions, and killing any remaining bottlenecks,” he wrote in a post on X.

The outage happened hours after bitcoin topped $60,000 for the first time since November 2021 and went on to approach $64,000 before rapidly dropping back down to $60,000. Its all-time high above $69,000 is now in sight.

Other crypto exchanges, such as Kraken, didn't report any technical problems.

This isn't the first time Coinbase is experiencing an outage due to heavy trading. The exchange went down briefly in May 2020 after bitcoin tumbled 10% in the span of 30 minutes. Before that, in June 2019, the same problem occurred when the cryptocurrency dropped $1,800 in 15 minutes.

UPDATE (Feb. 28, 2024, 18:18 UTC): Notes historical outages.

UPDATE (Feb. 28, 2024, 18:27 UTC): Notes that other exchanges didn't report any issues.

UPDATE (Feb. 28, 2024, 19:23 UTC): Adds Coinbase CEO's Brian Armstrong's post on X.