Chinese online retailer JD.com is staking a claim in China’s intensely competitive package-delivery market by opening its logistics network to parcels shipped by consumers and businesses.

When the Venta Maersk sailed out of Vladivostok late last month, the container ship was laden with far more than just a load of seafood.

Many importers scrambled to get ahead of the U.S. tariffs on Chinese shipments that kicked in Monday.