The Panama Canal is installing the last of 16 giant lock gates that are a key part of the waterway's multibillion-dollar expansion.

Tuesday's installation of the 4,232-ton gate at the Pacific Ocean entrance to the waterway means the most critical phase of the expansion can start in coming weeks: the flooding of the locks.

Panama in 2006 decided to build a wider canal to accommodate vessels capable of carrying 2.5 times the number of containers held by ships currently using the canal.

The expansion has been beset by a nasty battle over cost overruns with European builders and delays that have pushed back its expected opening by a year to April 2016.