An imminent merger of China's high-speed train manufacturers, China North Locomotive and Rolling Stock Industry (Group) Corporation (CNR) and China South Locomotive & Rolling Stock Corporation Limited (CSR), is boosting both companies' shares, which have jumped by the daily limit for three days in a row.

Their combined market value has overtaken Boeing, the world's largest aircraft manufacturer by market value.

According to an earlier announcement, the two companies will merge as the world's biggest train maker.

At Wednesday's close, CNR posted 389.6 billion yuan (62.9 billion U.S. dollars) in A-shares and 42 billion Hong Kong dollars (5.42 billion U.S. dollars) in H-shares, and CSR's A-shares hit 409.3 billion yuan and H-shares totaled 37.2 billion Hong Kong dollars. The companies' combined market value will total about 139 billion U.S. dollars after the merger, with 128.8 billion U.S. dollars being A-shares.

The Forbes Global 2000, an annual ranking of the top 2,000 public companies in the world, showed that Siemens, with a market value of 114.2 billion U.S. dollars, was the biggest rival of CNR and CSR last year. Other transport equipment manufacturing giants included Boeing, with a market value of 95.3 billion U.S. dollars, and Toyota, with a capitalization of 193.5 billion U.S. dollars.