In 2011, the U.S. Postal Service made special agreements with the national postal carriers of China and Hong Kong (and subsequently South Korea and Singapore) to allow tracking-enabled packages not exceeding 36" or weighing over 4.4 pounds to be sent to the U.S. for extremely low rates. They called this shipping option the ePacket, and the rates are so low that it's cheaper to ship small parcels from China to an American city than it is to send that same parcel domestically.*
On the territory of China, a parcel shipped via ePacket is sent by EMS China Post. It's delivered pretty fast for further export. Once it arrives at the destination country, the delivery is fulfilled by a local state-owned postal service as First Class Mail (which is USPS First Class Mail, if we say about the USA). Accordingly, an addressee receives a parcel in the nearest postal store.
In general ePacket shipping cost is cheaper than delivery via EMS China Post and a local postal service. In addition, delivery time is shorter. It takes about 15 days to reach the USA via ePacket.