BEIJING -- The Shenzhen Stock Exchange on Tuesday merged its main board with the SME (small and medium-sized enterprises) board amid efforts to unify business rules as well as supervision modes.

After 16 years of development, listed SMEs have converged with the main board in terms of market value scale, performance and trading characteristics, according to the exchange.

The merger is a natural choice to conform to the law of market development, and it is also an inherent requirement to build a concise and clear market system, the bourse said.

Three companies debuted on the Shenzhen main board Tuesday.

Issuance and listing conditions, investor thresholds, trading mechanisms, and stock codes and abbreviations remain unchanged after the combination.

Involving only adjustments in parts of business rules, market products, technical systems, and issuance and listing arrangements, the merger will have little impact on market operations and investors' transactions in general, the exchange said in February when China's securities regulator approved the merger.

Fixed-income products, futures, and options products would be mostly unaffected, and the Shenzhen-Hong Kong stock connect program would not be affected either, according to the bourse.