Australian biotech firm CSL is positioning itself as one of the world's biggest flu vaccine businesses, with a partial buy-out of Novartis.

CSL will become second largest in the world after buying Novartis's global influenza vaccine business in a new $US275 million ($312 million) deal.

CSL says combining its existing flu vaccine operations (bioCSL) with Novartis’s will enable it to make vaccines in the US, UK, Germany and Australia, for better ‘geographical diversification’.

The company expects to see sales of up to $1 billion per year in the next three to five years.

“The Novartis influenza vaccine business provides bioCSL with a global leadership position in an attractive sector we understand intimately,” said CSL managing director Paul Perreault in a statement.

“It will transform bioCSL by giving it first class facilities and global scale as well as product and geographic diversity.”

CSL announced a share buyback program earlier this month, but says the new deal will be funded by surplus cash.

The deal is undergoing relevant regulatory approvals, and is expected to be completed late next year.