Dublin-based pharmaceutical group Shire on Tuesday said it has bid $30 billion (27 billion euros) for US rival Baxalta to form a global biotech company focused on rare diseases.

"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," Shire's Chief Executive Officer Flemming Ornskov said in a statement.