Websites of major US airline companies American Airlines, Southwest Airlines, United Airlines and Delta Air Lines faced an outage early on Thursday, according to outage monitoring website Downdetector.

More than a thousand user reports indicated problems at Southwest Airlines, with over 400 user reports indicating the same for Delta Air Lines, according to Downdetector. That number was around 300 for the other two airline companies.

Southwest canceled nearly 300 flights on Wednesday and delayed more than 500 a day after it was forced to temporarily halt operations over a computer glitch.