GlaxoSmithKline said it fired staff in China for bribing officials in 2001 in a case that predates wider allegations of corruption for the British drugmaker in the country by more than a decade.

About 30 staff in GSK's vaccines business were dismissed for bribing Chinese officials, the Financial Times reported on Thursday, after they were found to be involved in bribing Chinese officials and taking kickbacks.

The emergence of the scandal could put the operations of Britain's largest pharmaceutical firm in China under even more scrutiny.

U.S. and UK authorities are already investigating GSK for a much bigger corruption scandal in China, involving what Chinese police have said were elaborate schemes to bribe doctors and hospitals.

GlaxoSmithKline said in a statement it had "zero tolerance" for unethical behaviour of any kind.

"We investigate any allegations put to us and take action where necessary," the company said on Thursday.

"The specific matters occurred more than 12 years ago. We believe appropriate investigation and action was taken at the time."

Chinese police said in May they had charged the former British boss of the drugmaker's China business, Mark Reilly, and other colleagues with corruption.

U.S. authorities are investigating GlaxoSmithKline for violations of U.S. anti-bribery laws in China following the corruption accusations.

Britain's Serious Fraud Office has also launched a formal criminal probe into the company.