US airlines have begun the arduous process of cancelling thousands of flights as they brace for the impact of Hurricane Irma. Operations centres at major US carriers are again in overdrive as they try to move as many passengers as possible before they’re forced to take aircraft out of the path of the category 5 hurricane. CNBC reported late Thursday US time that 4000 flights had been cancelled in Irma’s path. American Airlines is expecting more than 2200 cancellations over the weekend as it shuts down Florida operations in Miami, Fort Lauderdale, Fort Myers, Orlando , West Palm beach and other airports. The carrier has now issued a travel alert for more than 40 airports that allows customers to rebook without change fees. It has capped fees at $US99 each way for main cabin tickets and $US199 for premium cabin tickets in markets where seats are limited. It also announced a $US99 fare cap for those returning to the area up to September 17. “As many flights are already sold out, we encourage customers traveling out of South Florida to only go to the airport if they have a confirmed ticket,’’ American said in a travel alert issued late Thursday afternoon. Delta Air Lines added more than 3000 seats over Thursday-Friday to help customers evacuate and capped fares in all cabins $US399. The airline said it expected Miami, Ft. Lauderdale and West Palm Beach to close Friday night and operations to be cancelled Saturday and likely Sunday “pending updates from the airport authority”. “Orlando may see winds as high as 50 knots on Sunday night which may prompt the closure of the passenger tram system,’’ it said. Delta has expanded its fare waiver to include airports along the Georgia and South Carolina coasts. The airline attracted international attention after it sent a sent a flight into Puerto Rico ahead of the hurricane to pick up passengers. The Boeing 737 landed at San Juan in Puerto Rico’s north coast and flew out about 40 minutes later as winds started to gust at up to 31knots (57kmh). United also issued fare waivers affecting airports throughout the Caribbean and Florida and said it was re-timing flights to and from southern Florida from Saturday. Hurricane Irma is now being labelled the strongest hurricane ever recorded in Atlantic and has weakened only slightly after devastating several Caribbean islands. One notable aviation victim has been St Maarten's famous Juliana Airport. However, weather experts say the storm could be downgraded to Category 4 by the time it hits Florida.     .