Shares in engineering and construction group Kvaerner plunged to their lowest level since 1986 on Thursday after market sources said Nordic investment bank Carnegie downgraded the firm.
Kvaerner was trading at 47.50 crowns per share, down 3.5 crowns, when the Oslo bourse halted automatic matching of the shares to investigate price moves.
It fell further to a year low of 45.50 crowns per share, down 10.8 percent, when the bourse resumed matching.
In its report, Carnegie cut its recommendation to "reduce" from "accumulate", said sources, who declined to be quoted or named.