The Cala Portofino and its sister ship are berthed at Teesport
More ships could be mothballed at Teesport because of a decline in the shipping industry, according to operator PD Ports.
Two 600ft (185m) container ships, the Cala Portofino and Cala Positano, are currently berthed at Middlesbrough.
The booming economy of the past decade had seen a lot of new ships built, according to Martyn Pellew the Group Development Director for PD Ports.
But he said the recession meant there was now an overcapacity in shipping.
Mr Pellew said: "In the last five to 10 years there have been a lot of new ships built and they've been much bigger ships because you get economies of scale in shipping.
"The rather unprecedented downturn has meant there's been a bit of an overcapacity in shipping, and rather than have the ships run round the world empty - paying the crews and paying for fuel - the best thing is to put them on berths until such a time as the economy picks up."