NYSE Euronext shareholders have approved a merger with Deutsche Boerse to form the biggest stock exchange operator in the world valued at some $25 billion.

A merged Deutsche Boerse and New York Stock Exchange Euronext will own bourses in New York, Frankfurt, Paris, Lisbon, Amsterdam and Brussels.

'It's an important step in our merger project,' said NYSE Euronext chief executive Duncan L Niederauer after 65.6 per cent of shareholders voted in favour of the deal.

In Germany, Deutsche Boerse chief executive Reto Francioni hailed the vote, saying shareholders had clearly approved the new group's growth prospects and potential for value.

Deutsche Boerse shareholders will vote separately on July 13, with the tie-up expected to produce annual savings of 300 million euros ($430m).

Under the terms of their February 15 merger proposal, Deutsche Boerse shareholders will own 60pc of the combined, Netherlands-incorporated firm, and the German company will dominate the new board.

The new entity will control nearly 90pc of the markets for derivative investment instruments in Europe.

If Deutsche Boerse shareholders approve the deal, regulators will weigh-in next.European antitrust authorities launched their examination of the merger last week with a preliminary probe due to close by August 4.

Brussels must decide whether to authorise the operation, possibly with conditions attached to it, or launch a deeper investigation that could last several months. The longer option is more likely, observers said.

In March, European competition commissioner Joaquin Almunia said that the deal required a detailed study while the number two at NYSE Euronext, Dominique Cerutti, said that the firm was expecting an in-depth look from regulators.

The deal was threatened this year when Nasdaq OMX and IntercontinentalExchange launched a hostile, $11.3 billion bid for NYSE Euronext but the two firms walked away in May after US antitrust officials opposed the plan.