Five Indian airlines announced disruptions to their booking systems on Friday, matching widespread technical problems reported by flight operators around the world.
"Our systems are currently impacted by a Microsoft outage," IndiGo, the country's largest airline by market share, said in a post on social media platform X.
"During this time booking, check-in, access to your boarding pass, and some flights may be impacted."
National carrier Air India said its systems had been "impacted temporarily due to the current Microsoft outage", causing travel delays.
Budget operator SpiceJet said it had reverted to manual check-ins and boarding after "technical challenges".
"Our teams are diligently working with our service provider to resolve these issues promptly," the airline said.
Akasa Air and Vistara also reported outages.
Delhi Airport in India's capital said it was "working with all our stakeholders to minimise the inconvenience" to passengers.
The Press Trust of India news agency reported that passengers were "stranded" in the coastal holiday hotspot Goa as a result of a technical glitch with the airport's check-in system.
In Hong Kong, some airlines had been affected by an IT outage, as widespread technical problems were reported by flight operators around the world.
"A Microsoft outage that has disrupted the service of airlines worldwide is affecting some of the airlines at Hong Kong International Airport," the Airport Authority said in a statement.
"Flight operations at (Hong Kong's airport) have not been affected."
A message on flag carrier Cathay Pacific's website said that flight booking and redemption services were "currently unavailable".
Its subsidiary HK Express said self-service check-in facilities and departure control systems had been affected.
"Due to a global service outage of Microsoft, Navitaire, our global e-commerce system has been affected," the airline said on its official Facebook page.
HK Express said it had reverted to manual check-in processes after its website and mobile apps were affected.
In Washington, US air carriers including Delta, United and American Airlines grounded all flights early on Friday over a communication issue, according to the Federal Aviation Administration.
"All... flights regardless of destination" were grounded due to the "communication issues", the FAA said in a notice to airlines.
In Berlin, flights were suspended at Berlin Brandenburg airport in Germany on Friday morning due to a "technical problem", a spokeswoman told AFP as several countries reported massive IT disturbances.
"There are delays to check-in and flight operations had to be cancelled until 10:00 am (0800 GMT)," the spokeswoman said, adding however that she could not say when they would resume.
A large-scale outage also wrought havoc on IT systems across Australia on Friday, with the country's national broadcaster, its largest international airport, and a major telecommunications company reporting issues.
The disruption ahead of the first weekend of the school holidays in Berlin came as US tech giant Microsoft said it was taking "mitigation actions" after service issues.
The UK's biggest rail operator also warned of possible train cancellations due to IT issues on Friday morning.