PANAMA CITY, June 2 (AFP) – Leading users of the Panama Canal voiced outrage Tuesday at toll increases that take effect next year, call them outsized, unfair and ill-timed.

The Panama Canal Authority in April announced in April it would raise tolls. The hikes set to take effect January 1 vary by the type of ship and cargo, from 8-16 percent.

''Shippers have suffered from the decrease in traffic, and even now we face an uncertain future'' after the economic crisis of 2008, Julio de La Lastra, of the Shipbuilders' Association of Japan, told a hearing on the tolls.

''We respectfully oppose the proposed toll hikes completely, and we see them as of little or no positive use in terms of trade,'' he argued.

Canal administrator Alberto Aleman Zubieta however said: ''This is quite simple. No one likes the cost of anything to go up.''

Panama ''delivers a very important service to the world, and we should be allowed to be paid for the value of that service,'' he stressed.

The United States ships the most through the canal, almost 54 million tonnes a year; it is followed by China, with 25.6 million tonnes a year, and Chile with 11.1 million tonnes.

In fiscal 2009, the canal generated about two billion dollars in tolls of which it paid about 800 million dollars to government coffers.

Key users argue the hikes are above Panama's inflation rate, in addition to being ''perceived as coming at a bad time,'' according to Eduardo Salinas, of the Chilean embassy.

Work began in September to enlarge the canal by constructing a third set of locks to ensure that today's supersize container ships, cruise liners and oil tankers -- many of which are too wide for the canal -- will be able to navigate the waterway in the future.

The cost of the work has been put at some $5.2 billion, and should be complete by August 2014, a century after the canal's inauguration.

Since then a million ships have crossed the 80-kilometer (50-mile) canal, through which five percent of the world's trade crosses every year.

The third set of locks, parallel to the existing two, would accommodate massive vessels 366 meters (1,200 feet) in length, 49 meters (160 feet) wide and with a 15-meter (50-foot) draft.