US drugmaker Eli Lilly said it was "deeply concerned" about allegations it bribed Chinese doctors to prescribe its products, the latest accusations of malpractice by foreign firms in the country.

A former Eli Lilly sales manager claimed the firm paid at least 30 million yuan ($4.9 million) in kickbacks to doctors for promoting two insulin drugs in Shanghai and neighbouring Anhui province, the 21st Century Business Herald reported Thursday.

The whistleblower, using a pseudonym, said bribery was a "very common" practice at the company, which also offered doctors payments through speeches and conferences, the paper said.

"We are deeply concerned about the allegations made against Lilly China," the drugmaker said in an emailed statement late Thursday.

It admitted being aware of similar allegations last year and had conducted an "exhaustive" investigation through employee interviews, email monitoring and expense report audits.

"Although we have not been able to verify these allegations, we take them seriously, and we are continuing our investigation," the statement said.

Eli Lilly is the third foreign drug firm embroiled in corruption scandals in China, after similar accusations against Britain's GlaxoSmithKline (GSK) and France's Sanofi emerged over the past two months.

Authorities have detained four Chinese GSK executives and formally arrested a foreign husband-and-wife team of fraud investigators whose firm did work for GSK, after allegations that GSK employees used nearly $500 million in bribes to boost sales.

Chinese regulators have opened an investigation into Sanofi, state media reported earlier this month.

It is common practice in China for pharmaceutical firms to offer doctors and hospitals bribes to have their products used, industry insiders say.