Air India chairman Ashwani Lohani told NDTV that the "airline's passenger's system is down".

Highlights Air India system restored after shutdown for over 5 hours

Airline was unable to issue boarding passes to flyers at airports

Hundreds of Air India flyers were stranded at airports across the world

Air India's operations across the world were affected for over five hours this morning because of a problem in the airline's main server. Though the server has been restored, the shutdown left hundreds of passengers stranded at airports. Passengers complained about delayed flights and shared pictures and videos of crowded airports in Mumbai and Delhi. The airline said 155 flights will be delayed for an average duration of two hours till 8.30 pm today.

According to the national carrier, the server was down since 3 am due to which the airline was unable to issue boarding passes to passengers at airports across the world.

"The system has been restored. It has begun functioning. We regret the inconvenience that passengers had to face," Air India chairman Ashwani Lohani was quoted as saying by news agency PTI. "We are trying to regularise all the flights for the day. But there would be some delay of flights today. I am expecting a delay of around two hours. Because in morning, the whole system got disturbed," he added.

Mr Lohani said he expects normalisation of operations by tonight.

Air India's software solution is managed by SITA, a global airlines IT services major, which provides its check-in, boarding and baggage tracking technology.

"At least 2,000 people in Mumbai airport waiting because of the SITA software shutdown all over India," wrote Gayathri Raguramm, a Twitter user. She also shared a video from Mumbai airport showing flyers waiting in near the check-in area.

Atleast 2000 people in Mumbai airport waiting because of the SITA software shutdown all over India. pic.twitter.com/TzYYFLE5vz — Gayathri Raguramm (@gayathriraguram) April 27, 2019

Stranded at Mumbai airport since the last 3 hours. Apparently Air India servers are down. Asked the employees for an update, he laughed and said "Ab dekhte hain kab aayega" @airindiain — Bhavya_shree (@Bhavyas66424462) April 27, 2019

The massive crowd at the Mumbai airport has affected passengers of other airlines too, with many of them worried about missing their connecting flights.

British Airways responded to a flyer's tweet, saying, "...we can only advise to try and get through the airport as quickly as possible. If you do miss a connecting flight, the staff at the airport should do their best to assist."

Hundreds of Air India passengers were left stranded at many airports.

A similar incident took place on June 23 last year when a technical glitch in the airline's check-in software delayed 25 of its flights across India.

The average number of flights that Air India group, which also includes subsidiaries Alliance Air and Air India Express, flies daily are around 674.