LISBON, May 24 (Reuters) - Portuguese pulp and paper producer Navigator said on Tuesday its first-quarter net consolidated profit more than doubled thanks to price increases, but warned rising production costs will make the near future very challenging.

Navigator, which sells more than 80% of its output overseas in as many as 130 countries, said it netted 50.6 million euros ($54 million) in the quarter, compared with a net profit of 23.5 million euros in the same period last year.

Total sales grew 44.4% in the first quarter from a year ago to 492.2 million euros, "driven by a general rise in prices internationally."

Even though inflationary pressures have allowed it to jack up prices to its customers, Navigator is concerned that soaring commodity and energy costs may end up denting its profit margins and down the road lead to shrinking demand for its products.

In early January, the company raised prices for uncoated woodfree paper (UWF) by between 10% and 15% and two weeks later it increased prices for tissue paper by 15%, in reaction to huge cost increases in natural gas, chemicals, raw materials and logistics.

Navigator said that though it maintains "a strong order book", Russia's actions in Ukraine have triggered several risks, and "the near future looks very challenging, in an international context of extreme uncertainty and instability."

It fears that costs could remain at "historically high levels or even rise" further, and said strong inflationary pressures coupled with expectations of rapid rates hikes "could result in a global economic slowdown."

The company has focused on increasing efficiency to protect itself.

Earnings before interest, taxes, depreciation and amortisation (EBITDA) rose 72.3% in the quarter from a year ago to 121.6 million euros.

The operating margin - EBITDA/sales - went up to 24.7% in the first quarter versus 20.7% in the same quarter of 2021. ($1 = 0.9370 euros) (Reporting Sergio Goncalves, editing by Inti Landauro and Louise Heavens)