Shareholders of US pork giant Smithfield Foods have approved the purchase by Shuanghui International in what is shaping up as the largest acquisition of a US company by a Chinese firm.

Shuanghui, a leading Chinese meat processor, will pay $4.5bn in cash for the American company, which is the world's largest combined pig raiser and pork processor. Including Smithfield debt, the deal's value comes close to $7.1bn.

The deal received 96 percent of the votes cast at a special shareholders meeting on Tuesday, despite an earlier challenge by a key investor arguing the deal undervalued the company.

Smithfield president and chief executive Larry Pope called the deal "a great transaction for all Smithfield stakeholders, as well as for American farmers and US agriculture."

The deal, which aims to satisfy China's increasing appetite for pork, marries two of the world's largest pork producers and faced scrutiny over China's high-profile food safety failures, concerns over US pork supplies and US national security.

But earlier this month, the US Committee on Foreign Investment cleared the way for the deal, removing an important hurdle.

The transaction is expected to close by September 26.