JetBlue Airways, the New York-based low cost carrier, announced on Wednesday that it would begin flying across the Atlantic Ocean, from London to Kennedy International Airport and Boston Logan International, in 2021.

The company’s chief executive Robin Hayes said the new routes are a response to passenger demand.

JetBlue is known for having a loyal customer base, but entering the hypercompetitive trans-Atlantic market is still likely to be a challenge. The three major airlines in the United States — American Airlines, Delta Air Lines and United Airlines — have multiple flights each day between the East Coast and Britain. The market is further crowded by two British carriers and low-cost Norwegian Air.

“This is not going to be an easy win for JetBlue,” said Henry Harteveldt, the founder of Atomosphere Research Group, an industry analysis firm. “The big airlines especially are going to bring flamethrowers to a game of rock-paper-scissors.”

Mr. Harteveldt expects these airlines already flying between the East Coast and London will strongly compete with JetBlue on price. Many of the more established carriers will be at an advantage, he said, as they have more daily flights and more capacity than JetBlue will, which ultimately means more flexibility for their passengers. But increased competition is still a boon to fliers.