A Boeing 737 jetliner is pictured during a tour of the Boeing 737 assembly plant in Renton, Washington February 4, 2014. [Photo/Agencies]

BOC Aviation, the leasing arm of Bank of China, has placed the biggest order in its 20-year history for 80 Boeing medium-haul passenger planes, weeks after lessor SMBC Aviation ordered 115 Airbus jets.

The shopping spree by leasing companies comes as they ride a boom in aviation financing and see strong demand from airlines. Seeking to keep lean balance sheets, airlines are increasingly turning to lessors to upgrade fleets to fuel-efficient aircraft.

Singapore-based BOC Aviation, one of the world's leading lessors, said the order was for 50 Boeing 737 Max 8 planes and 30 Next Generation 737-800 aircraft, which will be delivered from 2016 to 2021.

The order, which also includes two 777-300ER long-haul wide-body planes, has a value of $8.8 billion at list prices, Boeing said. Last month, SMBC placed an order worth about $11.8 billion for Airbus planes. Buyers typically receive an undisclosed discount on the listed prices of jets.

The order is part of BOC Aviation's strategy to build its fleet for the next seven years. The company had a fleet of 251 delivered aircraft as of June 30.

"Following the successful placement of the 50 Next Generation 737 aircraft that we ordered in 2006, this is a continuation of our commitment to be responsive to airline customers which are expanding or replacing older fleets," said Robert Martin, managing director and CEO of BOC Aviation.

Asia-Pacific is the top region for aviation growth. The region's customers are expected to buy about $2 trillion worth of planes over the next 20 years, or 39 percent of global sales of $5.2 trillion, according to Boeing's latest forecast.

Lessors such as BOC Aviation place their aircraft with airlines globally, and are increasingly important customers for the plane makers as their share of global fleets grows.

The order for the upgraded, re-engined variant of the Boeing narrow-body jet follows BOC's deal for 43 of Airbus Group NV's (AIR.PA) A320 family of aircraft, including seven of the re-engined A320neo planes, at the Farnborough airshow in July.

COMAC gets order boost at major airshow	BOC Aviation orders 43 Airbus A320 planes