SAN DIEGO -- Lifeguards were warning scuba enthusiasts to take extra precautions in the waters off La Jolla Shores Wednesday following a report of a strong underwater current that pulled about a half-dozen divers into deep water and made it difficult for them to surface.

The group of divers reported getting caught in the unexplained undertow while roughly 30 feet underwater about 7:30 a.m., San Diego lifeguard Lt. Andy Lerum said.

They said the phenomenon lasted about 10 minutes and rapidly pulled them 30-50 feet deeper. Several described hanging on to the edge of a deep submarine canyon in the area to keep from being dragged farther down.

The divers eventually surfaced, feeling the grip of the current lessen as they reached the top, Lerum said. There were no injuries.

Lifeguards had no immediate explanation. They notified Scripps Institute of Oceanography personnel, who also were in the dark about what likely caused the anomalous marine condition.

"So we're kind of baffled a little bit about it," Lerum said in the early afternoon.