The idled container ship fleet shrunk by nearly one million 20-foot equivalent units in the past six months as ocean carriers launched new services to keep pace with rising cargo demand in the summer peak shipping season.

The jobless fleet stood at 549,000 TEUs on May 24, down from a peak of 1.522 million TEUs at the beginning of December, according to Paris-based consultant Alphaliner.

The faster-than-expected reduction in idled tonnage has created shortages of ships above 4,000 TEUs capacity.

The idled fleet is set to fall further to 450,000 TEUs by the end of June as carriers rapidly re-activate laid-up ships of over 4,000 TEUs, Alphaliner said.

"The reduction in idled tonnage is all the more remarkable as it comes on the back of 1.12 million TEUs of newbuildings delivered over the past 12 months," it said.

The idled fleet excludes some 30 ships with a total capacity of 270,000 TEUs which have already been built and will be delivered when their owners have resolved financing issues with shipyards.

Several are due to be delivered in the coming weeks and are already booked to join new or existing services.

The idled fleet is set to increase at the end of the peak season in September-October when cargo demand contracts and shipyards deliver more ships, according to Alphaliner.

The decline of the euro against Asian currencies also will have a negative impact on cargo volumes on the Asia-Europe trades.

Alphaliner forecasts the idled fleet will reach one million TEUs by the end of the year.