A survey of dozens of Europe's top business executives shows their optimism is waning as trade tensions and other geopolitical uncertainties cloud the outlook for the global economy.

A poll of 50 CEOs and chairmen carried out by German research group ZEW on behalf of the European Round Table for Industry, a trade association, shows that while the expectations for business remain slightly positive overall, employment and investment prospects are down.

Only about 25% of executives expect to increase investment in Europe in the next six months, with less than 50% expecting to create more jobs.

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The findings highlight economists' concerns that the stresses on manufacturing and trade created by the U.S.-China trade war and Brexit are affecting the wider economy.

Some experts estimate that the world economy will grow this year at its slowest since the global financial crisis. Yet unemployment is low in developed economies and services industries are holding up so far. Should the trouble in trade and industry begin to drag down other parts of the economy, the global slowdown could be more severe and painful.

The report by the ZEW surveyed executives of major companies like consumer goods maker Nestle, telecoms company Ericsson, steelmaker ArcelorMittal, among others, and was seen by The Associated Press ahead of its release Friday.

The European Round Table for Industry said the findings should encourage the incoming European Commission to focus on bolstering innovation, particularly in the digital and environmental sectors, and further integrating the economies of the European Union.

"While European industry's current outlook is broadly positive, there are real structural challenges inhibiting companies from investing, creating jobs and competing with the rest of the world," said Martin Brudermueller, chairman of chemicals conglomerate BASF and the head of the ERT's group on innovation.