The Norwegian Petroleum Safety Authority said it was worried about "what would happen if something snaps" given the high degree of work on the continental shelf.
Ingvill Hagesaether Foss, a safety director at the agency, said it's up to individual companies to determine whether they have the expertise to work safely offshore.
"Sufficient expertise and capacity are crucial for maintaining the level of safety," she said in a statement.
The Norwegian Petroleum Safety Authority said work meant to extend the life of offshore fields could add another layer of burden to normal maintenance procedures.
Total petroleum reserves on the Norwegian continental shelf last year were estimated at about 80 billion barrels of oil equivalent. About 60 percent of that hasn't been extracted.
The Norwegian government said it expected investments in the oil and natural gas sector to reach $30 billion by the end of the year.
Norwegian Energy Minister Ola Borten Moe had said natural resource production should increase in the coming years. Active investment in existing fields, however, is needed to realize the full potential.