The airlines, therefore, have been issuing boarding passes manually since 5.30 pm, the official added.
The AAI owns and manages more than 100 airports - including the Netaji Subhash Chandra Bose International Airport in Kolkata - across the country.
"The Internet server has been down since 5.30 pm and it is likely to start working from 10.30 pm today (Monday). Around 25 flights have been delayed in between 5.30 pm and 9 pm by an average time of 20-25 minutes," said the AAI official.
The official added that the IT team of the AAI is working diligently to resolve the issue.