WARSAW (Reuters) - Poland's top oil refiner Orlen's first-quarter net profit slumped 70% to 2.77 billion zloty ($704.82 million) due to the impact of a windfall tax and a weaker refining performance, missing expectations.

Earnings before interest, tax, depreciation, and amortisation (EBITDA) in the quarter fell by 53% year-on-year to 7.73 billion zlotys, while revenues declined to 82.33 billion, the company said on Wednesday.

Analysts' estimates were for net profit of 3.24 billion zlotys.

Orlen's payment of a windfall tax used to stabilise gas prices rose by 4.2 billion zloty to 7.7 billion in the first quarter. The contribution will amount to about 15 billion zloty in the full year, Orlen said.

First-quarter operating profit in the refining business

slumped by 52% to 1.9 billion zloty, due to weaker margins and volumes.

Orlen said it needs to speed up investments to meet its strategic goals by 2030.

"In order to achieve strategic goals, some investment projects require significant acceleration," CEO Ireneusz Fafara said. He said Orlen would publish an updated strategy by the end of 2024.

The company said its capital expenditure in the first quarter stood at 6.4 billion zlotys compared with a full-year target of 38.6 billion.

($1 = 3.9301 zlotys)

(Reporting by Anna Koper and Marek Strzelecki. Editing by Jane Merriman)