The number of containerships waiting at the ports of Houston and Charleston, S.C., reached new pandemic highs as importers looking to avoid bottlenecks on the West Coast encounter growing congestion in alternative gateways.

The world’s largest shipping hubs are suffering elevated levels of congestion as containers pile up at seaports from Singapore to Greece’s Piraeus.

The backlog of ships outside the twin ports of Los Angeles and Long Beach — America’s largest gateway for ocean freight — is poised to worsen.