Construction workers in northeast Florida have unearthed a piece of 19th-century history buried beneath the oldest city in the United States.

Florida Department of Transportation crews were digging as part of an ongoing drainage improvement project in downtown St. Augustine on October 5 when they discovered a nearly intact vessel hidden in the dirt, the department said in a news release.

The shipwrecked boat -- found more than 8 feet below ground -- was fully removed and in wet storage by Wednesday, department officials said.

The fishing boat was found on State Road A1A near the Bridge of Lions in the city known as the "oldest continuously occupied settlement of European and African-American origin" in the US, according to the historic city's website.

DOT officials say they believe the vessel dates back to around the mid- to late 1800s.

"We believe the vessel may have sunk unexpectedly and, over time, was silted in," said Greg Evans, the department's District 2 secretary, in a statement. "That is why it was preserved so well -- it was encapsulated in soil and mud, so there was no air contact for it to decay. It's truly an incredible find."

The transportation department contracted SEARCH (Southeastern Archaeological Research Inc.) as part of its drainage improvement project due to the historic nature of the St. Augustine area, officials said.

SEARCH, which says it has the nation's largest maritime archaeology team, is a cultural resources management company made up of archaeologists, architectural historians, conservators and other experts.

The company sends archaeological monitors to construction sites like the one in St. Augustine where historical finds may be uncovered, according to James Delgado, the senior vice president and exploration sector leader for SEARCH's station in Washington, DC.

Sam Turner, a principal investigator and maritime archaeological expert for SEARCH, was on site when the tip of an excavator bucket digging in the trench exposed the water-soaked wood of the unexpected discovery, Delgado said in an email to CNN.

"Sam asked the operator to stop, got into the hole and gently scraped with his trowel to reveal a gently curving outline of what he immediately identified as the edge of the hull, with a displaced piece of timber from a frame," Delgado said.

Delgado, whose archaeological experience includes working with buried ship excavations, joined Turner in Florida to recover the historic vessel.

"Detailed hand mapping and measurement was done, but the main focus was measurable, three-dimensional photo-modeling of all major construction features as well as measured photomosaics of the hull throughout the careful excavation and disassembly of the vessel," Delgado said.

"We used water and gentle troweling and gloved hands to wash and brush off the mud to expose the fragile wood," he added.

Investigators believe the flat-bottomed boat, possibly made of soft wood such as pine and cedar, was originally about 28 feet long. It measured 19 feet in length when it was found, according to Delgado.

"The stern was missing when exposed by the excavation, consumed by marine organisms long ago," he said, describing it as a well-built boat possibly constructed by "the people who owned and worked it."

SEARCH experts say the boat may have been abandoned near the end of its working life on what were once the banks of a local river and bay.

It was likely buried for "as much as a century" before crews found it, Delgado said.

"Many waterfronts that have changed over time through landfill have buried boats and ships," he said. "That being said, these are still rare finds in the world of maritime archaeology."

Before the boat is relocated to a permanent home, the next step is to stabilize the vessel, according to Ian Pawn, Florida DOT District 2 cultural resources manager.

"When an object this well-preserved is discovered in wet conditions, archaeologists have to work quickly as the drying of wood will begin the decaying process," Pawn said in a statement.

"The pieces will be observed in wet storage to stabilize as we determine future preservation efforts," he said.