Authorities in the eastern Chinese city of Shanghai say they have seized 2.4 tons of methamphetamine in one of the country's largest drug busts.

Shanghai police said Thursday on their official microblog that they arrested 28 people in the joint operation with police from the southern province of Guangdong, where the drug lab was discovered.

Illegal drugs remain a major problem in China despite tough laws, including the death penalty for offenders.

Last year, Guangdong police used 3,000 armed police officers in a drug sweep that seized nearly 3 tons of methamphetamine and 23 tons of raw materials to manufacture the stimulant drug.