Deng Zhisong, an antitrust attorney with Beijing-based Dacheng Law Office, said that an international merger needs to be studied case-by-case and countries will reach different antitrust conclusions about one transaction.

"Given the size of the transaction, the process might be very time-consuming, but I think the results would be relatively optimistic," said Deng.

For the US and European markets, where the rail and mass transit industries have become highly concentrated, new suppliers like the Chinese companies with cost advantages will be beneficial for full competition.

That is not considered a negative factor by local regulators, so they might also obtain clearance in these markets, said an analyst who declined to be identified due to the sensitivity of the issue.

Huang Yong, deputy head of the expert advisory group of the State Council's Anti-monopoly Committee, said it is difficult to forecast the results of these reviews.

The analytical methods adopted by antitrust agencies are very complex, and they conduct a thorough study of companies' shares in each market segment, such as light rail, subways, high-speed systems, commuter services and locomotives, Huang said.

This case should also be reviewed by China's antitrust agencies, said analysts.