The recovery of four giant plastic pipes washed up on the Norfolk coast may take "several weeks", the Maritime & Coastguard Agency (MCA) has said.
Norwegian manufacturer Pipelife Norge said the 8ft (2.4m) diameter pipes broke loose from a tugboat when it was hit by a container ship last month.
The beached segments, the longest of which measures 1,574ft (480m), washed up at Winterton and Sea Palling.
Eight pipes still at sea were "secured and under control", the MCA said.
The pipes were being towed to Algeria for use in an energy project by MTS Viscount, before being hit by the Samskip Courier vessel on 19 July.
Pipelife Norge said up to seven tugboats and two diving teams would assist the salvage operation.
However, the MCA said returning the pipes to Norway "may take several weeks" and would involve them first being relocated to an offshore site near Lowestoft.
"The circumstances surrounding the parting of the pipes from their tow is subject to further investigation and the MCA is unable to comment further," the MCA added in a statement.
Other than their physical presence, it said the pipes were not believed to pose any other danger of, or potential for, pollution.
Jordan Grebby, senior maritime operations officer for UK Coastguard, said: "We have received several 999 calls regarding the pipes and sent teams to the area after reports were received that children were playing on or inside the pipes.
"We would like to issue a safety message to those in vicinity to keep at a safe distance until the salvage operation is complete.
"If you see anyone in close proximity to the pipes we would ask that you call us on 999 and ask for the coastguard."