Budget airline Vanilla Air said 10 passengers on one of its flights from Hong Kong entered Japan without going through immigration due to an error at Narita International Airport on Sunday night.
The company had contacted the 10 passengers by Monday evening and requested that they clear immigration at the airport.
The transport ministry issued a strong warning to the airline and demanded that it report the cause and preventive measures to the ministry by Friday.
This is the second time Vanilla Air has been given such a warning by the Land, Infrastructure, Transport and Tourism Ministry.
In a similar incident in April 2016, 159 passengers from Taiwan didn't clear immigration due to a mistake by Vanilla at Narita.
"I believe preventive measures have worked well, but I feel very responsible that it has occurred for a second time," Vanilla Air President Katsuya Goto said at a news conference Monday in Tokyo.
After the flight arrived at 10:13 p.m. Sunday, a total of 169 passengers got on three buses from the plane to an airport terminal.
But a 63-year-old driver of one of them mistakenly took 34 passengers to an arrival gate for domestic flights instead of one for international flights, according to the carrier.
The mistake surfaced after some of the passengers told a staff member at the terminal building that they did not go through immigration procedures.
Of the 34 passengers, 24 cleared immigration, customs and quarantine after being notified by Vanilla Air and other staff, but the remaining 10 entered the country without going through the necessary procedures.
The airline was unaware of the mistake until it was reported by the passengers, as no staff from the airline was on the bus, it said.
