HANGZHOU - A parcel explosion that injured two people in east China's Zhejiang province on Sunday has raised concerns about the lack of supervision over the country's fast-growing express industry.

The explosion happened Sunday night in an office of Yuantong Express Company in downtown Hangzhou, Zhejiang's provincial capital. Two female employees were slightly hurt and were sent to hospital.

After a day's investigation, Hangzhou police arrested suspect Wang Jianjia late Monday.

Wang confessed he had sent the parcel containing crackers and fireworks to his former employer, a musical instrument store owner in Hangzhou who fired him last year, in an attempt to vent his resentment.

But the parcel exploded before it was delivered.

Wang has been detained and is being further investigated.

Shanghai-based Yuantong Express Company, founded in 2000, is one of the leading express delivery service providers in China.

Its Hangzhou office resumed business Monday morning, before the cause of the explosion was found.

"It seems everything has returned to normal and the incident will soon be forgotten," said a man who runs a fastfood restaurant nearby. "But who knows? Maybe next time a package will explode in my hands."

Shao Zhonglin, vice secretary of China Express Association, said the accident was a result of lax supervision in China's express industry.

According to China's postal law, express delivery companies are required to conduct safety checks of every parcel they receive from their customers before packaging and delivery.

But the law has not been executed properly, as many couriers Xinhua interviewed said they seldom check the content of the packages.

A Yuantong employee surnamed Wang said he handled more than 100 packages every day and it was impossible to look into every package.

"Many customers are also reluctant to have their packages examined, and I don't want to lose my business by insisting on the safety check," Wang said.

Fueled by the nation's online buying spree, the express industry has experienced rapid development, topping 10 million parcels a day at the end of last year.

It was the third largest volume globally after the United States and Japan, according to statistics released by China's State Post Bureau (SPB).

Yet analysts warned that behind the bubble were poor service quality and inadequate supervision.

Apart from the safety concerns, delayed deliveries, damages and even losses of packages caused by inadequate operation have more than once pushed express companies into the center of public outrage.

Having recognized these problems, China's postal sector is working to strengthen supervision over the express industry, said Shao.

On August 11, the SPB issued a set of regulations to standardize operation of express delivery business. It's also working on measures to evaluate the service of the express companies.

"The package explosion has sounded a safety alarm of China's express industry, so greater efforts must be made to improve services," said Shao.