Tests with ships will begin in mid-2015 on a new set of locks that are a key component of an expansion of the Panama Canal, the waterway's chief said on Sunday.

The 100-year-old canal, which is major global trade artery, is in the midst of a massive expansion that will allow the world's largest tankers to pass through the isthmus.

The expansion, which involves building a third set of locks onto the 50-mile (80-km) waterway, was originally scheduled to be completed this year, but has been delayed several times, in part due to a dispute earlier this year because of about $1.6 billion in cost overruns.

The deadline for completion is now January 2016.

On Sunday, Panama Canal Administrator Jorge Quijano said the locks would likely be ready, holding water, by April or May of next year.

"We hope to start a series of tests with the locks next year in the month of July or August," Quijano said after overseeing the arrival from Italy of a shipment of four new gates for the locks.