Business at the State Ports Authority continued to grow at a double-digit clip last month, but that pace will be tough to match next year, the maritime agency's top executive said.

Dock workers at the Port of Charleston handled the equivalent of 164,672 20-foot-long shipping containers in October, up 17 percent from the same month last year.

Since July 1, when the fiscal year began, the SPA's volume has increased 14 percent to 633,347 boxes. Breakbulk shipments, which are too big or heavy to be transported in containers, are up 23 percent over the same four months to about 287,000 tons in Charleston and Georgetown.

"It's exports, it's export, it's really across the board," said Jim Newsome, president and chief executive officer of the SPA.

Newsome said that he expects the port's growth rate to moderate as the calendar year winds down.

"As we get toward the holidays, that's a tradition slow time anyway," he said.

Also, Newsome said, the gains from 2014 will be difficult to sustain in 2015 on a percentage basis because the this year's volume numbers will become the new benchmark.

"It just a function of math," he said. "One year's great results become next year's tough comparisons."

Newsome added that container ports in the South Atlantic are expected to outperform most other parts of the country, citing strength in manufacturing along with the region's overall population growth.

In the Upstate, the SPA reported brisk business at its year-old Inland Port, where Norfolk Southern trains haul containerized cargo to and from Charleston. The authority recently signed a deal with a new user and another company is testing out at the 100-acre rail yard, Newsome said.

The $50 million Spartanburg County investment has "exceeded our expectations," he said,

Since July 1, demand has been running about 1.5 times higher than projections, according to the SPA.

"I'm not saying we're low-balling the numbers. We're just seeing more customers up there doing stuff than we planned," Bill McLean, the SPA's senior vice president of operations, said Wednesday.

In response, Norfolk Southern recently added a Saturday train, its sixth assigned to the Greer-Charleston run.

Contact John McDermott at 937-5572.