LONDON, July 27 -- Norwegian aluminum and power company Norsk Hydro ASA (NHY.OS) Tuesday posted an 80% rise in operating profit and kept its outlook unchanged.

"Higher realized aluminium prices, improved performance from Hydro's alumina and raw materials operations and higher downstream sales volumes all made a significant contribution to underlying results for the quarter," the company said in a statement.

Net profit was 503 million Norwegian kroner ($81.8 million) for the three months to March 31, compared with a profit of NOK211 million during the same period a year earlier, as revenue climbed 16% to NOK19.78 billion from NOK17.12 billion.

Hydro's closely-watched underlying earnings before interest and tax was NOK1.11 billion, compared with NOK618 million a year earlier. The underlying results strip out gains or losses on derivatives, impairment charges, income or expenses from disposals and other one-time items.

Analysts had forecast a net profit of NOK594.9 million and underlying earnings of NOK914.2 million on revenues of NOK19.72 billion, according to a Dow Jones Newswires/Factset survey of nine analysts.

Norsk Hydro reiterated its expectations for 12% growth in demand in its main markets this year.

The company's shares closed Monday at NOK34.95, down 22% from the start of the year.