Hundreds of firefighters were involved and officials said two of them had to be treated at the scene for smoke inhalation.
"I can't believe after all we went through . . . it's heartbreaking, devastating," said Seaside Park Police Chief Francis Larkin, referring to the devastation left in the area a year ago by Hurricane Sandy. "I think I'm gonna wake up and it'll be a bad dream."
Larkin said firefighters would continue dumping water on a 19-block stretch for 24 to 36 more hours.
In a 10 p.m. briefing, Ocean County Fire Coordinator Brian Gabriel called the four boardwalk blocks that burned "a war zone." He said that the fire was 70 percent contained, with no threat of it spreading, but that firefighters continued to douse hot spots.
Gabriel said 300 to 400 firefighters from every department in Ocean County as well as departments from Atlantic, Cape May, Mercer, and Monmouth Counties were deployed.
The speed with which the flames engulfed the boardwalk, fanned by 30 m.p.h. winds, presented a major challenge. Firefighters dug two trenches ahead of the fire to try and stop it. The second one, at Lincoln Avenue, eventually held the flames.
Several buildings collapsed and a condominium sustained minor roof damage, resulting in evacuations, he said.
Seaside Park Mayor Robert Matthies called the catastrophe "the worst boardwalk fire I've ever seen in all my years."
In a news briefing in Seaside Park before the conflagration was brought under control, Gov. Christie noted the strenuous efforts made to rebuild the area from Sandy's blows a year ago and said when he heard of the fire, he exclaimed to his staff, "I feel like I want to throw up."
He vowed to linger on the scene and said he might help provide updates.
In a statement, Christie's Democratic opponent in the gubernatorial race, State Sen. Barbara Buono, called the fire "an unconscionable tragedy" and said she "was overwhelmed with a profound sense of sadness."
Seaside Park's boardwalk wasn't as badly damaged by Hurricane Sandy as Seaside Heights', though the storm did extensively damage Seaside Park's Funtown Pier.
On Thursday, the amusement pier again bore the brunt, this time of fire.
The spot where the fire apparently started - Kohr's Frozen Custard - also was gone.
Lee Maniscalco, 43, who walked what remained of the boardwalk with his wife, Andrea, late Thursday, noted that he was a friend of the Kohr's owner, who he said was himself a volunteer firefighter.
"I feel for him. . . . After all the blood, sweat, and tears that people put into rebuilding, we were all holding our breath for another hurricane. No one expected this," he said, staring at the smoke pouring from the charred Funtown Pier.
By late afternoon the fire had spread from Seaside Park north into Seaside Heights and jumped across Ocean Avenue, which runs parallel to the boardwalk, scorching buildings there.
For a time, officials closed the Seaside bridge leading in and out of the resort, allowing only emergency vehicles and fire trucks to enter. Dozens of fire companies from throughout Ocean and Monmouth Counties responded.
When she heard dozens of fire trucks whizzing past her home in the Pelican Island section of Berkeley Township, Susan Polcino said she crossed the bridge into Seaside Heights and witnessed crews trying to pull up sections of the boardwalk - some recently replaced - to stem the fire, but to no avail.
"The fire was coming so fast, they didn't get many of them up," Polcino said of the boards.
The scene was heartbreaking for the woman who has lived in the region most of her life.
"I'm sick to my stomach seeing this," said Polcino, 52.
Polcino said the wind along the coast was "fierce" and continued to fan the massive blaze.
"A friend of mine who lives here in Pelican Island who hasn't been able to move back into her house since the storm because of the damage was renting in Seaside. She just called to tell me she is being evacuated again because of the fire," Polcino said. "It's so sad."
The Red Cross said it had 12 volunteers on hand to assist emergency responders, but had not been asked as of late in the day to help find emergency housing for any evacuees.
"We know that emotions are running high with this situation, and we will be there to assist with refreshment and emotional support and anything else we can offer residents and first responders," said Laura Steinmetz, a spokeswoman for the American Red Cross South Jersey Chapter.
Contact Jacqueline L. Urgo at 609-652-8382 or firstname.lastname@example.org. Read her blog "Downashore," at inquirer.com/downashore. Follow on Twitter @JacquelineUrgo.