Education bosses in Los Angeles voted Tuesday to work towards a complete ban on the use of smartphones in the city's schools.

The move came as the governor of California, the most populous state in the US, voiced support for restrictions on the devices and as concerns grow about their impact on the mental health of young people.

The Los Angeles Unified School District Board of Education, which manages the second biggest school district in the country, ordered staff to devise a plan to prohibit cell phones and social media throughout the school day.

"Schools that have...already implemented a phone-free school day report incredible results -- kids are happier, they're talking to one another, their academics are up," said board member Nick Melvoin, who proposed the ban.

"And so I really think this is an idea whose time has come."

The resolution cited research indicating excessive cell phone use was associated with increased stress, anxiety, depression, sleep issues, feelings of aggression, and suicidal thoughts in adolescents.

It says eliminating phone and social media usage during the day has been shown to increase scores on standardized tests and final exams, gains that are "equivalent to an additional hour of instructional time per week."

The LAUSD vote, which would affect 600,000 students, comes after the US surgeon general, the country's top doctor, called for warning labels on social media platforms, which he said were incubating a mental health crisis.

"Adolescents who spend more than three hours a day on social media face double the risk of anxiety and depression symptoms," Dr Vivek Murthy wrote in a New York Times opinion piece.

"The average daily use in this age group, as of the summer of 2023, was 4.8 hours," he noted.

Hours before the LAUSD vote on the resolution, which instructs staff to come up with a plan within the next four months, California Governor Gavin Newsom threw his weight behind a state-wide effort to clamp down on smartphone use among schoolchildren.

"As the Surgeon General affirmed, social media is harming the mental health of our youth," he said.

"When children and teens are in school, they should be focused on their studies - not their screens."

A bill pending in the California state legislature would require school districts to adopt measures prohibiting or limiting students' use of phones while at schools.

"I look forward to working with the Legislature to restrict the use of smartphones during the school day," said Newsom, a father of four.

Florida, whose governor Ron DeSantis is an arch-rival of Newsom's, banned student cell phone use last year.

Similar plans are afoot in Oklahoma, Kansas, Vermont, Ohio, Louisiana and Pennsylvania.