Horizon Lines, the second-largest shipper serving Hawaii (Matson is first), announced Tuesday that it needs more time to file its annual financial report because of an "extremely complicated" debt restructuring under way that could affect the company’s ability to continue operations.

The North Carolina-based ocean cargo transportation company restructured significant debts last year but is still working to complete a tentative restructuring of another $228 million of debt. That’s contingent on restructuring charter obligations for five ships after terminating service between the mainland, Guam and China in November.

Horizon said it expects it will complete the transactions. But if it can’t, the company said, it expects an independent auditor will express substantial doubt about Horizon’s ability to continue operations.

The firm is seeking an extension from the Securities and Exchange Commission to file its annual report on or before April 10 along with fourth-quarter financial results. The report was due Monday.

Horizon released some preliminary operating results Tuesday for its fiscal fourth quarter ended Dec. 25. The company said it expects a $6.4 million operating loss on revenue of $264.3 million for the period, which compares with a $32.6 million operating loss on revenue of $256.1 million in the same quarter a year earlier.

Shares of Horizon stock slipped 20 cents to $6.30 Tuesday after the announcement.