Rivera starred for six seasons in Glee, the wildly popular musical television series set in a US high school that ended in 2015. — Photo Naya Rivera Facebook

LOS ANGELES — Glee star Naya Rivera is missing and feared drowned at a California lake, where divers, patrol boats and helicopters resumed their search for the US actress on Thursday.

The operation to locate the 33-year-old – a "possible drowning victim" – began at first light at Lake Piru, around an hour's drive northwest of Los Angeles.

Rivera, best known for her role as high school cheerleader Santana Lopez in Glee, disappeared Wednesday after renting a boat at the camping and recreational hotspot with her four-year-old son.

The child was found around three hours later by another person out on the lake "asleep and with his life vest on," Ventura County Sheriff's Office spokesman Eric Buschow said.

"We believe she did go in the lake," he told a press conference.

The lake has been closed to the public while the search continues, with dive teams from across the region arriving to assist. More than 80 personnel were involved in the operation.

Rivera starred for six seasons in Glee, the wildly popular musical television series set in a US high school that ended in 2015.

She more recently appeared in Devious Maids, and web series Step Up: High Water.

Rivera had put up a photo of her and her son on Twitter on Tuesday, alongside the phrase: "Just the two of us."

Thousands have left comments below the post, many offering their prayers.

Rivera and the boy's father, actor Ryan Dorsey, divorced in 2018.

The Glee cast has been struck by tragedy before.

Actor Mark Salling took his own life in 2018, weeks before being sentenced for possession of child pornography.

Canadian castmate Cory Monteith died in July 2013 of an overdose of drugs and alcohol. — AFP