A late-night fishing trip in the hope of bagging a kingfish or a few snapper turned into a four-hour battle to land a 3m shark for two Auckland fishermen.

Ralph Mailau and Daniela Paila were fishing the shallow waters of a sandbar off Puketutu Island in the Manukau Harbour early yesterday when the fish struck, and from then on they had to swap the fishing rod back and forth between them every 30 minutes.

"It may have been even less than that," said Mr Mailau. "It was hard work."

The fish was caught from Mr Paila's 3.5m dinghy, which they anchored soon after the shark was hooked. When they finally brought the fish alongside, they realised it was too large to lift into the boat. "It would have been too dangerous. It was too big, too strong," said Mr Paila.

Instead the men waited for the tide to recede and leave them and their catch high and dry on the mudflats of the harbour. They then used the anchor to kill the shark and threaded a rope through its mouth and gills in order to haul it on board. When the tide came back in and refloated them the men motored home.

Having launched at 11 the night before, the men finally made it back to the Mangere Bridge boat ramp about 8am. Family and friends came down to see the prize.

The men got an inkling there was something big in the area when two days ago, fishing at the same spot, they broke a number of fishing lines on large fish. This time they returned with heavier fishing tackle.

"I thought it must have been a kingfish," said Mr Paila. "But as soon as I tried to bring it in, I knew it wasn't."

The men have cut shark steaks which they say they will enjoy "well into January".