Traffic at the ports of Los Angeles and Long Beach rose 10 percent in April compared with the same month last year, according to figures released Thursday.

Port of Los Angeles spokesman Phillip Sanfield said the jump was in part due to an improving economy. He also said retailers appeared to be importing holiday season goods earlier this year to cover their bases should port labor negotiations fail and affect shipping.

More than 706,000 containers went through the Port of Los Angeles in April, up 10.3 percent from April of last year and the highest number since September. Imports rose 11 percent year-to-year, while exports rose 8 percent. Empty containers sent overseas to be filled for imports were up 10 percent. Container volume for the first four months of the year is up 8.2 percent over the same period last year.

Meanwhile, nearly 570,000 containers moved through the Port of Long Beach in April, up 9.7 percent from April of last year. Imports rose 12 percent year-to-year, while exports rose 6 percent. Empty containers were up 9 percent. Container volume for the first four months of the year was up only 1 percent.