A Marlborough teenager has pleaded guilty to clubbing to death 23 seals near Kaikoura last year.

Jason Trevor Godsiff, 19, of Renwick, admitted charges of possessing an offensive weapon and wilfully ill-treating the seals by beating them to death when he appeared in Blenheim District Court this morning, The Marlborough Express reported.

He was remanded for sentencing on September 13.

Co-accused Jemaal Peter Roy Large, 35, a driver from Wairau Valley, is yet to enter a plea to the same charges.

The fur seals were beaten to death with a steel pole at Ohau Point, north of Kaikoura, late last year, the court was told.

Some of the dead seals were just a few days old and other live seals also had injuries, suggesting they too had been hit.