Specialty biopharmaceutical firm Shire has made an offer of around $30bn to acquire Baxalta, a drugmaker subsidiary of Baxter.

Shire has proposed to pay $45.23 per Baxalta share, representing a 36% premium to its stock price on 3 August.

Baxalta has confirmed that it received highly conditional and unsolicited proposal from Shire to purchase all of its outstanding common shares in an all-stock transaction.

"Both firms are predicted to deliver product sales of $20bn in 2020."

Baxalta board chairman Wayne Hockmeyer said: "The board today reaffirmed its conclusion that Shire’s proposal significantly undervalues Baxalta and its attractive prospects for growth and value creation, and that a merger at this time would be severely disruptive at this very early stage of Baxalta’s existence as a public company and presents a significant and real risk to value creation for our shareholders."

According to Shire, the combination will provide platform for growth, with over 30 planned product launches and rare diseases portfolio with around 50 projects.

Through their combined pipeline, both firms are predicted to deliver product sales of $20bn in 2020, said Shire.

Shir CEO Flemming Ornskov said: "We believe the proposed combination of Shire and Baxalta would be strategically and financially attractive for both of our companies, accelerating our respective growth ambitions and creating the leading global biotech company in rare diseases."

Baxalta is involved in developing, manufacturing and commercialising therapies for orphan diseases and underserved conditions in haematology, oncology and immunology.

The firm’s therapies are available in around 100 countries worldwide.