A 13-year-old boy who fell into a drainage pipe during an Easter outing at a Los Angeles park was rescued alive after an overnight search of the underground system, US authorities have said.

The boy spent at least 12 hours in the sewerage system before he was found.

"We located Jesse Hernandez alive and talking," fire captain Erik Scott, said, adding: "We were able to give him a cellphone to even contact his family members (who) as you can imagine are overwhelmed with joy."

The search began at around 4.30pm on Sunday when the Fire Department received reports that the boy had fallen about 8 metres down a pipe at the city's sprawling Griffith Park.

The Los Angeles Times reported that Jesse and his cousins were jumping on wooden planks in an abandoned maintenance building when one of the planks broke and he fell.

The drainage system is part of a network of pipes 1.2 metres in diameter that run parallel to the Los Angeles River and crosses under motorways.

Numerous agencies joined the Fire Department, including the sanitation and engineering bureaus. Cameras that are normally used for pipe inspections and can both float and crawl were sent into the pipes.

About 731 metres of pipe had been inspected when Bureau of Sanitation workers opened a hatch to lower a camera near the intersection of two roads and found Jesse.

He was treated by paramedics and taken to a hospital for a medical evaluation.