Spot rates for shipping containers from Asia to northern Europe plunged 20.5 per cent to US$934 per TEU in the week ending last Friday, according to the Shanghai Containerised Freight Index, reports Reuters.

Last week's fall comes after an 88 per cent hike in the index two weeks ago after Maersk said it would increase rates by $900 when the index was languishing at just under $700 per TEU.

But it was the largest ever weekly decline on the world's busiest freight route since the index began recording rates in 2009. A level below $1,000 is widely seen as a loss-making level for container shipping companies.

Container freight rates have so far increased in 12 weeks this year but fallen in 33 weeks.

Maersk Line, the global market leader with nearly 600 boxships, recently cut its forecast for global demand in container transport to grow three to five per cent from a previous 4 to 5 per cent expectation.

"It's difficult for me to see how market conditions could improve for shipping companies since new vessels are still coming to the market from shipyards," said Sydbank analyst Jacob Pedersen.

At the end of the third quarter of 2014, the global container vessel fleet amounted to 18 million TEU, an increase of 5.4 per cent compared to a year ago.