UPDATE 1-Norwegian Air and JetBlue plan transatlantic partnership

Victoria Klesty and Terje Solsvik

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OSLO, Oct 17 (Reuters) - Norwegian Air and New York's JetBlue Airways have agreed to form a partnership that will allow customers to book flights on each others' aircraft, with a planned startup in mid-2020, lifting Norwegian Air's shares.

Norwegian Air has shaken up the market for transatlantic travel with cut-price fares that challenge traditional carriers such as IAG's British Airways, but has so far lacked a domestic U.S. partner.

The deal, if completed as intended, will let passengers combine low fares in a single booking for flights between the Americas and Europe, the companies said in a statement.

"Customers will have the possibility to book connecting flights on both airlines' websites by combining the best of our complementary and expansive networks," they added.

Norwegian Air shares were up 6.4% at 35.80 Norwegian crowns at 1036 GMT, outperforming an Oslo benchmark index up 0.62%. (Editing by Gwladys Fouche; Editing by Mark Potter)