Shanghai Airlines, the mainland's fifth-largest airline, said it will begin a thrice-daily Hong Kong-Shanghai service on November 28, bringing the number of carriers on the route to four.
Cathay Pacific Airways, which announced its plans to return to the route two months ago, is not scheduled to start its once-daily service until December 1.
The two cities are now served 16 times a day by Hong Kong Dragon Airlines and 14 times a day by China Eastern Airlines.
Shanghai Airlines said its flights will depart Shanghai Pudong Airport at 9.15am, 1.25pm and 4.45pm and depart Hong Kong at 1.05pm, 5pm and 8.30pm.
Cathay Pacific has announced that its flight will leave Shanghai at 10.35pm daily except Saturday when it will leave at 3.05am. The turnaround will depart Hong Kong at 6.40pm daily except Friday when it will leave at 11.35 pm.
However, market sources say Cathay has won approval to swap its 10.35pm Shanghai departure with the 10pm slot of its subsidiary Dragon Cargo Airlines. Cathay declined to comment.