The teenager had been celebrating Easter with family at Griffith Park in Los Angeles when he fell into the drain and was swept into the series of interconnecting sewage pipes.
Hernandez was with at least two family members, reportedly his cousins, around 4:30 p.m. Sunday when the wooden plank beneath the 13-year-old broke, causing him to fall into the 4-foot-wide pipe.
Authorities with the Los Angeles Fire Department said he was cold, wet and hungry, but was "alert and talking" after the terrifying ordeal.
Scott said the sanitation crews played a major role in finding Jesse.
Searchers doggedly inspecting a complex drainage system network found Jesse Hernandez, 13, at a Burbank location around dawn. The pipes parallel the Los Angeles River and cross under freeways.
After an accident like Jesse's, rescuers say the likelihood of someone being found safe diminishes by the hour.
Rescuers in Southern California on Monday morning spotted and extricated a boy who was stuck in a maze of drainage pipes for about 12 hours, authorities said. Such cameras are regularly used to inspect pipes for fix.
Rescuers finally found Jesse after seeing images of handprints on a sewage pipe.
Sanitation workers opened the maintenance hatch and saw Jesse about 11 feet down in the pipe.More news: Tony Ferguson Withdraws From UFC 223, Max Holloway Named Replacement
A sanitation official said one of the cameras had showed "some hand markings on the sewer itself - inside - (and) it appears that he was trying to get out".
"The first thing they heard is, 'Help!'" Hagekhalil said.
Hernandez is receiving "decontamination", medical aid and was being taken to a local hospital, according to LAFD.
Officials studied maps of the closed sewage pipe system, which stretches a total of some 6,400 feet, and sent a camera attached to a flotation device down a pipe.
Firefighters were "also using gas meters and all available equipment to safely conduct this on-going search", the statement said. The boy was given a cellphone to call his family, "who, as you can imagine, are overwhelmed with joy", the Los Angeles Fire Department captain said.
Erik Scott made the announcement at 5:41 a.m. The cameras "have more advanced capabilities including lighting and the ability to attach to a pontoon which will crawl along the pipe".
The pipes are filled with 2 feet or more of liquid that moves at 15 miles per hour, the fire department said.
More than 100 LAFD firefighters and park rangers were scrambled.