UPDATE 1-China Southern unit to buy 20 Boeing 737s

(Adds delivery dates of planes)

SHANGHAI, April 20 (Reuters) - China Southern Airlines (600029.SS: Quote, Profile, Research), the country's largest airline by fleet size, said on Sunday its subsidiary Xiamen Airlines had signed a contract with Boeing Co (BA.N: Quote, Profile, Research) to buy 20 Boeing 737 airplanes.

The 20 planes have a list price of about $1.5 billion, but Xiamen Airlines negotiated a lower price, China Southern said.

The subsidiary would pay for the planes, due to be delivered between April 2014 and October 2015, with its own funds and with bank loans.

It was not immediately known if the 20 planes were a new order for Boeing, or if their purchase had been previously announced by the Chinese government under one of its umbrella deals with foreign aircraft makers.

China Southern also said that it planned to issue 4 billion yuan ($572 million) of short-term bills of up to one year, to raise operating funds. It did not give other details of the issue. (Reporting by Andrew Torchia, editing by Maureen Bavdek)