SINGAPORE - Singapore budget carrier Jetstar Asia and Australia's Qantas are expanding their codeshare arrangements to offer customers more choice and greater frequencies in Asia.

With immediate effect, the Qantas flight code will be available on another 142 services operated by Jetstar Asia, bringing the number of weekly codeshares between the two carriers to 349.

This means for example that a passenger with a Qantas ticket can book a Sydney-Singapore-Bangkok flight in a single transaction.

The first leg will be operated by Qantas and the second, by Jetstar Asia.

The codeshare agreement between the two carriers also provides customers with more opportunities to access Frequent Flyer benefits, the airlines said on Thursday.

Qantas now operates 44 weekly flights from Australia to Singapore.

Passengers who travel on Qantas codeshare flights operated by Jetstar can opt for through check-in and lounge access at Changi Airport - for those who are eligible.

Qantas codeshare passengers also receive a hot meal on flights over 90 mins and a muffin on flights under 90 mins, plus water, tea or coffee.