Import cargo volume at the United States' major retail container ports is expected to be up 13 percent in March compared with the same month a year ago, and double-digit increases are expected to continue through the summer as the US economy begins in improve, the Canada Business News Network reported.

"These numbers show that retailers continue to anticipate improvements in the US economy," National Retail Federation vice-president for Supply Chain and Customs Policy Jonathan Gold said.

"This is very different from the past two years when merchants were continually cutting their imports in an effort to manage inventory."