Takeda Pharmaceutical Co. said Wednesday it has raised its offer for acquiring Irish drugmaker Shire Plc. to $64 billion as it extended the deadline for what would be the biggest-ever overseas purchase by a Japanese company.

Takeda raised its offer price per share to 49 pounds from 47 pounds in its fifth attempt to buy Shire, which would make the deal worth around 46 billion pounds.

The deal would eclipse SoftBank Group Corp.'s 2016 purchase of British semiconductor designer ARM Holdings for 24 billion pounds -- the largest foreign acquisition by a Japanese company.

(Takeda Pharmaceutical Co.'s headquarters in Tokyo)

The Japanese drugmaker said it and Shire extended the deadline for talks on the acquisition to May 8. It had been due to expire Wednesday.

Takeda's share price briefly fell 9 percent from the previous day on the Tokyo Stock Exchange as concerns grew about the hefty cost of the deal.

By acquiring Shire, known for its strength in medicines for rare diseases, Takeda aims to counter overseas rivals, banking on Shire's strength in the key U.S. market.

On Tuesday, Reuters reported that the two companies plan to announce a basic agreement, citing people familiar with the matter.

The Irish company "has indicated to Takeda that it would be willing to recommend" the latest proposal to its shareholders, according to Takeda.

Takeda has been aggressively buying pharmaceutical companies in Europe and the United States. It acquired U.S. drugmaker ARIAD Pharmaceuticals Inc. in 2017.