"We made a mistake but we look forward to welcoming you on board with your ticket issued", a tweet to customers said.
After news broke, attention turned to whether Cathay will honour the tickets, which typically sell for HK$35,000 ($6655) in business or HK$55,000 ($10,500) in first class for a return flight. Sign-up now and enjoy one (1) week free access!
If you spot a remarkably low fare, it is best to book the flight on your credit card, as the process to be sent e-tickets is quicker and more likely to happen before the mistake is noticed.
Cathay Pacific has admitted it made a mistake when it sold business-class tickets at a huge discount.
Other flights from Vietnam to U.S. airports were also offered at drastically reduced rates. Ticket prices weren't available for August on the website.
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It was not clear how many tickets had been sold and Cathay Pacific did not immediately respond to requests from the BBC.
"Hope this will make your 2019 "special" too!"
In October, Cathay Pacific acknowledged hat its computer system had been compromised, exposing the personal information and travel histories of up to 9.4 million passengers. The airline honored its mistakes and covered all bookings.
Big Apple-based IT professional Vincent Lee Chun-fai, 42, bought two first-class tickets on Tuesday, but told the Morning Post that his flight from Da Nang to NY - which cost $1,600 - was canceled without explanation.
Also in 2018, the company's plane went viral after the company name, Cathay Pacific, was shown misspelled as Cathay Paciic on its side.
In October previous year, it also revealed a major data breach affecting 9.4 million passengers that leaked passport numbers, credit card numbers, and email addresses.