Reports from Vanuatu say two people were prevented from leaving the country for trying to have two different passports stamped.
The immigration says under Vanuatu's immigration law, a person is only entitled to enter and to exit a country with a passport and not two.
The individuals in question had a Chinese and a Vanuatu passport, which they had obtained last week after the Citizen Commission in Port Vila had granted them a certificate.
Immigration officials say it is the first such case they have come across.
Last month, the Chinese embassy in Port Vila asked Vanuatu to report Chinese people who get Vanuatu passports because they automatically lose their Chinese citizenship.
Vanuatu changed its laws to allow dual citizenship this year and set up a company in Hong Kong, Capital Investment Immigration Plan, to sell access to Vanuatu citizenship.