Suppliers to U.S. aerospace and semiconductor firms face worsening rare earth shortages, with two turning away some clients, industry insiders said, weeks before U.S. President Donald Trump is expected to meet his Chinese counterpart Xi Jinping for a summit in Beijing. The shortages center on rare earths such as yttrium and scandium, niche members of the family of 17 elements, which play tiny but vital roles in defence technology, aerospace and semiconductors and are almost entirely produced in China. While Beijing has allowed many rare earth exports to resume since it imposed restrictions in April, shipments of these materials still rarely make it to the U.S. despite the October detente with Washington, Chinese customs data show.