BEIJING (Reuters) - Air China signed an agreement on Friday to buy 100 C919 jets from state-owned planemaker COMAC to be delivered by 2031, the country's biggest airline said.

The planes are worth about $10.8 billion at list prices but COMAC has agreed a discount, Air China said in a Shanghai Stock Exchange filing.

Air China also reported a first-quarter net loss of 1.7 billion yuan ($235 million).

($1 = 7.2464 Chinese yuan renminbi)

(Reporting by Ella Cao, Ethan Wang and Ryan Woo; editing by Jason Neely)