The search for former Glee star Naya Rivera is continuing more than 24 hours since she was reported missing at a lake in Southern California.

The 33-year-old had taken a boating trip with her four-year-old son Josey Hollis on Wednesday, who was later found asleep in the rented boat alone.

Lake Piru is around 56 miles north-west of central Los Angeles, and police are continuing a huge search operation in and around the location.

Local police, the Ventura County Sheriff's office, said on Thursday that Rivera was presumed to have drowned, and said the effort to find her was now classed as a 'search and recovery operation'.

READ MORE: Search launched for Glee actress Naya Rivera after star goes missing in Lake Piru, Southern California

The cops shared CCTV footage from the dock, which shows Rivera's boat departing.

Sergeant Kevin Donoghue revealed it may be weeks before a body is found.

Sgt Donoghue said: “If the body is entangled on something beneath the water, it may never come back up.”

He added: “There’s no way to really say. We’re putting our best foot forward to try and locate her, we’re using all the assets that are available to us, we’re using technology like Sonar.”

Sgt Donoghue said experts involved in the search know the lake “inside and out,” adding: “We’re relying on their expertise to help us in that endeavour. We’re going to do everything that we can to find her.”

Rivera’s boat was found drifting in the northern part of the lake, with her sleeping son on board. She was nowhere to be seen.

HeraldScotland: The pontoon at Lake Piru, California, where Naya Rivera,33, rented a pontoon boat.The pontoon at Lake Piru, California, where Naya Rivera,33, rented a pontoon boat.

Josey is safe and with family. Police have since released the 911 call raising the alarm.

The caller, a woman whose husband was one of the first people to find the child, mistakenly identified the four-year-old as a girl.

The lake is closed while the search is carried out, Sgt Donoghue said. Diving teams and air operations will stop at nightfall before resuming in the morning.

Rivera’s family are waiting anxiously nearby for news, police said.