A 911 caller issued a chilling warning moments after the Saturday night bomb that rocked Chelsea — saying, “There will be more.’’

“I’m looking at the explosion down the block. There will be more,” the unidentified male caller threatened, law enforcement sources told The Post on Sunday.

As the suspect behind the terrifying blast that injured 29 people remained on the loose, officials revealed similarities between the pressure-cooker bomb that blew up on West 23rd Street, a similar undetonated device found on West 27th Street, and the pipe bomb that exploded hours earlier at the Jersey Shore.

All three bombs were fitted with old-school, mobile flip phones as their triggering devices — and one source said officials suspect the same person planted the New York and New Jersey devices.

On Sunday night, sources told CNN that surveillance footage showed a man dragging a duffel bag with wheels near the site of the explosion on West 23rd street — around 40 minutes before the blast occurred.

Another video shows the same man, wheeling around what appears to be the same duffel bag, on West 27th Street about 10 minutes later, the sources said.

The individual can be seen placing the bag where cops later found the unexploded bomb. After he walks away, the video shows two men removing a white garbage bag — containing the pressure cooker — and leaving it on the sidewalk.

Investigators are trying to determine the relationship between the three men.

A handwritten letter, a portion of which is in Arabic, was found inside a plastic bag that had held the West 27th Street device, sources said.

Meanwhile, a sketch artist was called in Sunday night to work with two witnesses who told cops they saw a man who was carrying a suitcase and seemed out of place on West 32nd Street about 30 minutes before the Chelsea blast, sources said.

Both Manhattan bombs were similar in design to those used in the deadly 2013 Boston Marathon attacks, which were built according to instructions from al Qaeda’s online Inspire magazine, sources said.

In other developments:

Mayor Bill de Blasio said a “bigger than ever” number of NYPD cops would hit the streets in response to the bombing and the UN General Assembly, where President Obama is set to speak Tuesday. Gov. Andrew Cuomo said he was deploying an extra 1,000 state troopers and National Guard members across the state.

Democratic presidential nominee Hillary Clinton issued a statement “strongly” condemning the “apparent terrorist attacks” in New York and New Jersey, and a multiple stabbing at a mall in St. Cloud, Minn.

A Manhattan woman said she called 911 after spotting the bomb that didn’t explode in Chelsea, recalling what looked like “a kid’s science experiment” near her home when a friend called with news of the blast.

The unexploded Chelsea bomb was taken to the NYPD firing range at Rodman’s Neck in the Bronx, where it was blown up when cops were unable to dismantle it late Sunday afternoon, sources said.

Evidence from both the New York and New Jersey bombings was being sent for analysis at the FBI lab in Quantico, Va., Cuomo said.

Both of the Chelsea bombs were built with pressure cookers, using Christmas lights as fuses, sources said.

That method is the same one that brothers Tamerlan and Dzhokhar Tsarnaev used for the bombs they detonated near the finish line of the Boston Marathon on April 15, 2013, killing three people and wounding more than 260.

But the Tsarnaevs used parts from remote-control cars as triggering devices and black powder from fireworks as explosive fuel.

In addition to cellphone triggers, the Chelsea bombs — which were packed with nails and ball bearings — contained Tannerite as the explosive material, sources said.

Tannerite is the brand name of a compound created in 1996 for use in exploding targets that “produces a water vapor and a thunderous boom” when shot with a high-power rifle, according to the manufacturer’s website.

Explosives experts who examined the remains of the Chelsea blast believe the bomb was placed inside a Dumpster that was torn apart and blown more than 130 feet across the street, sources said.

The impact of the landing is believed to have bent some of the Dumpster’s steel inward, sources said. That mangling had initially led investigators to suspect the bomb had been placed outside the container.

In addition to vowing that more bombs would be used to strike the Big Apple, the 911 caller warned that attackers would also open fire with guns, a source said.

Officials were investigating the validity of the caller’s claims.

Police Commissioner James O’Neill said he was “of course” concerned that no one had yet been busted.

“I know we’re going to find out who did this and they’ll be brought to justice,” added O’Neill, who marked his second full day succeeding former top cop Bill Bratton.

The two witnesses who saw a possible person of interest in the case were dining at the Krush bar and grill on 32nd Street when they noticed the man, sources said.

They called 911 around 11 a.m. and were brought to 1 Police Plaza for several hours of interviews before the sketch artist was summoned, sources said.

Passers-by in Chelsea described feeling under siege by the unsolved attack and threats of more to come.

“I feel afraid. My school is not too far from the explosion,” said art student Kaz Cheng, 28.

“I’m terrified that I may be the next victim if it happens again around here.”

Neighborhood resident Ben Brooks, 34, said it was “definitely unsettling not knowing who this person is or their motives. “

“People are freaked out. But in a city this large, it would be like finding a needle in a haystack,” he said.

Retired mechanic Gus Hanwerker, 61, of the Bronx, noted that “New York is very vulnerable.”

“There is so much room to do bad things. If it isn’t a terrorist, it could be one of our legions of unhinged people,” he added.

Additional reporting by Shawn Cohen, Shari Logan and C.J. Sullivan