India's aviation regulator has pulled up an airline for leaving behind passengers on the tarmac in the southern Indian state of Karnataka.
A flight by Go First, previously known as Go Air, took off from the airport in Bengaluru city, leaving more than 50 passengers forgotten in a bus.
Reports said the travellers had checked in their baggage and had boarding passes in hand.
The airline said it was investigating the incident.
Go First apologised to passengers who complained on Twitter but has yet to explain what caused the confusion.
The Bengaluru-Delhi flight took off at 06:20 on Monday even as several passengers were still on one of its buses on the tarmac.
"The ground staff was checking whether the flight took off," Sumit Kumar, one of the passengers, told news channel NDTV. "Initially, they said the flight will return."
After the flight left, angry passengers tweeted about their experience, criticising Go First for its "negligence".
The passengers tagged the airline, the federal aviation minister and the prime minister's office in their tweets.
Go First, responded to them, saying: "We regret the inconvenience caused."
A representative of the airline later told the Deccan Herald newspaper that the incident was being "investigated" but declined to comment further.
News agency ANI reported that 53 passengers were later accommodated on a different airline's flight while two others received refunds for their tickets.
India's aviation regulator, the Directorate General of Civil Aviation, "has sought a report from the airline and will take appropriate action", an official told the news agency PTI.
The incident is the latest in a series of recent complaints against airlines in India.
Last week, the pilot and crew of an Air India flight were derostered for their mishandling of a drunk passenger who urinated on an elderly woman.