A fire that ripped through a 120-foot-long fishing ship docked along downtown San Diego’s waterfront sent a cloud of thick, black smoke billowing over the harbor Friday and continued burning into Saturday.

The fire began around 9:40 a.m. as the vessel was docked at 750 North Harbor Dr., about one-third of a mile from Seaport Village. The smoke moved quickly through the air and could be seen all along the San Diego Harbor and from some parts of downtown, including the towering One America Plaza building.

NBC 7's Mackenzie Maynard reports from the San Diego Harbor where a fishing vessel caught on fire Friday morning.

The sight caught the attention of locals and tourists walking along the waterfront, many of whom stopped to gaze as fire crews descended on the ship.

San Diego Fire-Rescue Department (SDFD) spokesperson Monica Munoz said in the initial search of the ship, crews did not find anyone on board.

A fire ripped through a 120-foot-long fishing ship at the San Diego Harbor Friday, sending thick smoke into the air. NBC 7's Liberty Zabala reports.

Firefighters could be seen running up and down the dock as sirens blared in the background. At one point, flames were shooting from a porthole, with several firefighters surrounding it.

Raw video of a fire that ripped through a 120-foot ship at the San Diego Harbor on Friday.

Chris Weber, Assistant Chief of Emergency Operations with SDFD, said the fire appeared to have sparked in the ship’s lower deck levels. His crews were trying to gain access to those levels, which proved arduous.

Weber said the initial attack went well, but as the blaze intensified, firefighters had to back out, regroup and launch a coordinated attack. SDFD crews were being assisted by U.S. Coast Guard officials and crews from the Harbor Police Department who approached the burning ship from the water in their agencies’ emergency boats. Crews from other agencies were also en route.

[G] San Diego Fire-Rescue Crews Battle Ship Fire Near Seaport Village

About 45 minutes into the ordeal, Weber said close to 100 responders were battling the ship fire including a command staff and 20 to 25 fire apparatus. He planned to swap out crews as firefighters grew tired.

The assistant chief said ship fires are difficult to manage due to a number of challenging factors.

“These ship fires are very dangerous,” Weber told NBC 7. “If you think about it, it’s almost like a high-rise building sitting on its side. We practice and train for it as part of our normal thing but, as you can see, they are difficult. We have to pull lines all the way down to the end of the pier so that they can get into the ship.”

BREAKING: We're seeing flames shooting out of the side of the ship now. Several firefights on board. Stay w #NBC7 pic.twitter.com/cH3QTrdI4z — Liberty Zabala FOX 5 (@Liberty_Zabala) September 29, 2017

Weber said ladders were placed around the ship so firefighters could get on and off as needed. They also had to set up rescue crews in case a firefighter, outfitted with heavy gear, were to fall into the water.

“[These ships] are a solid steel vessel, so it’s hard to breach doors and get through. And then you’ve got heat that’s being channeled up through very tight ways, so the guys have to fight through all that heat to actually get down and put the fire out,” Weber added.

As of 10:30 a.m. Friday, Weber said the conditions appeared to be getting better and that firefighters would soon gain the upper-hand.

About 40 minutes later, however, SDFD officials said they had decided to switch the attack strategy from offensive to defensive, and all firefighters were being pulled off the boat. News helicopter video showed fire crews spraying down the ship from aboard other vessels surrounding it in the harbor.

BREAKING @SDFD changing tactic once again battling Norton Sound fire. They are now removing firefighters from vessel, letting it burn #NBC7 pic.twitter.com/vsCIZdEHOT — Liberty Zabala FOX 5 (@Liberty_Zabala) September 29, 2017

The blaze had been upgraded to a third-alarm response. In addition to the SDFD, Harbor Police Department and U.S. Coast Guard, crews from the Coronado, National City, and Chula Vista fire departments were also helping or heading to the scene.

Harbor Police Department Chief John Bolduc said the agencies made a unified decision to pull firefighters off the ship because it was no longer safe to fight the flames on board.

As of 11:40 a.m. Friday, the fire remained active inside, and Bolduc said officials hoped it would burn itself out within a few dozen hours.

More shots of the fishing boat fire near Seaport Village happening now. Second alarm fire that broke out at 9:31 this morning. pic.twitter.com/YWSLBZ0gL3 — SDFD (@SDFD) September 29, 2017

Due to the water being sprayed on the vessel, Bolduc said the ship was beginning to tilt. Adding more water to the ship could cause it to sink, but Bolduc said crews would continue to find ways to cool the blaze from the outside. He said once the fire burns out, and it is safe to go in, firefighters will access the decks.

SDFD Chief Brian Fennessy said the fire was located too deep within the ship to safely send firefighters into those decks for the time being.

He said with the flames, smoke and surrounding steel materials combined, it was likely about 1,000-degrees inside the ship.

At around 3 p.m. Friday, the fire began kicking back up, with flames shooting through to the upper deck of the vessel and heavy, black smoke permeating the air. Burnt pieces of the boat could be seen falling into the water.

Video shot by NBC 7 of the fire on a fishing ship docked at the San Diego Harbor kicking back up at around 3 p.m. Friday. Burnt pieces of the vessel could be seen falling into the water at this time. Officials plan to let the blaze burn itself out.

Bolduc said the last time they let a boat burn itself out was about two years ago when a fire tore through a boat on a dry dock. That fire took 51 hours to burn out.

Weber said crews did not find anyone on board during a primary search of the vessel.

The blaze scorched the vessel overnight, as firefighters kept a watchful eye. Munoz said crews remained at the scene all night, rotating monitoring duties every three hours and checking mooring lines every hour to make sure they didn't burn.

SDFD officials would re-evaluate the situation at 6 a.m. Saturday and determine how to staff the fire at that time.

On Saturday morning, the blaze was still burning as heavy smell of smoke continued clouding the waterfront.

Some surrounding business in Seaport Village temporarily closed due to the smoke. SDFD and U.S. Coast Guard crews remained at the scene monitoring the fire. An agency, NRC, contracted by the Coast Guard was testing the water around the boat and looking into the air quality and possible environmental impact, if any, of the ship fire.

The ship is emblazoned with the name "Norton Sound," and appears to be a fishing vessel. The ship had been docked there for several months.

Weber said officials were trying to contact the ship's owners Friday. On Saturday, Munoz told NBC 7 that the owners of the ship had been notified and were en route to San Diego from Mexico.

NBC 7 reached out to Norton Sound Enterprises, LLC/E&E Foods on Saturday, a Seattle-based company that once held minority ownership on the vessel. The director of sales said the ship was sold this past spring to someone in Mexico, though he couldn't confirm the owner's name. The new owner brought the ship to San Diego and docked it at the waterfront.

The cause of the fire is under investigation; no injuries were reported.