Affluent Chinese have discovered a safer place than under the mattress to keep their valuables - bank vaults.

Bank safe-deposit services have grown ever more popular as individuals accumulate wealth and seek safe storage.

Businessman Yang Liming believes banks are a safer place than home to keep valuables like jewelry, gold bullion, bank-deposit books, wealth-management contracts and property-ownership certificates.

"Bank vaults are underground and guarded," said Yang.

"And banks are a lot tougher to break into than an ordinary home," he said.

Safe-deposit boxes are usually arranged in underground vaults, where gaining access requires customers to undergo a fingerprint check, verify their identity and provide a password to gain access to their box.

In addition, two keys are required to open each box, with one held by the customer and the other by the bank.

Rental fees vary according to box size and range from several hundred to several thousand yuan a year.

The minimum box size is small enough to store an apple, but just right for a small jewelry collection.

There are also larger options to house bigger items like paintings, antiques or other works of art.

The most popular box has about the same area of an A4 piece of paper, which is a good match for important documents. The annual rental fee for this size of box is 600 yuan ($87.9).

"All of the boxes of this size have been rented out, so right now all we have available are smaller or larger ones," said a lobby manager at Beijing's Yayuncun branch of the Bank of Communications.

"Anyway, not many people own antiques, so most use deposit boxes to keep important documents like property ownership certificates and bank deposit books," said Zhang.

Most banks in first-tier cities like Beijing and Shanghai, as well as provincial capitals in second-tier cities rent out safe-deposit boxes, but normally only in large branch offices.

Banks began offering deposit boxes several years ago, but at that time few customers expressed any real interest.

To promote their use among wealthier clients, some banks - including China Construction Bank - used to provide free safe-deposit services to VIP customers.

Starting in 2008, as these services grew in popularity, banks switched tactics and started charging VIP customers, but at reduced rates.

"Our customers are usually rich businessmen in their 40s or 50s, so as personal wealth has grown, these individuals are willing to pay a small sum to keep their valuables safe," said Qu Jian, personal banking manager of a branch of Industrial and Commercial Bank of China in Shenyang, Liaoning province.