The bomb blast injured at least three people and damaged some 40 buildings. No deaths have been confirmed but authorities were examining tissue found at the blast site that they believe could be human remains

Authorities have been searching a two-story suburban house in the Nashville area as they probe the huge blast that ripped through the downtown of the southern US city on Christmas morning. Police and federal agents were scouring the charred site of a Christmas Day explosion in Nashville on Saturday.

Investigators have also been evaluating the possibility that the blast was likely the result of a suicide bombing, according to a report in CNN.

They said they were sifting through more than 500 leads and tips and that sweeps of the area found no further explosive devices.

Following up on these 500 leads, local police and agents from the FBI and US Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) were searching a two-story, red-brick house on Bakertown Road in Antioch, Tennessee, 11 miles (18 km) southeast of Nashville, paying particular attention to its basement.

The bomb blast injured at least three people and damaged some 40 buildings. No deaths have been confirmed but authorities were examining tissue found at the blast site that they believe could be human remains.

Police say the blast was an "intentional act" but the motive remained unclear and FBI behavioural analysts were involved in the investigation.

US media reports said a 63-year-old "person of interest" was identified in connection with the explosion, which came from a parked motorhome that blared a warning minutes before it blew up.

No one has been arrested, but "information developed during the course of the investigation led us to this address", an FBI spokesman said in an interview with the Nashville Tennessean newspaper outside the home being searched. 

At a separate press conference, authorities on Saturday declined to name a person of interest in connection with the explosion, but CBS News reported that the investigation has honed in on 63-year-old Anthony Quinn Warner, who recently lived at the Bakertown address. 

According to a document posted online, on November 25 he signed over the property to a woman in Los Angeles at no cost to her. The document was signed by Warner, but not by the woman.

Other media reports said neighbours had previously spotted a motorhome outside the residence that was being searched Saturday by authorities, and that it appeared to be similar to the one that exploded in Nashville.

The investigation included some 250 FBI agents, analysts and other staff.

The governor toured the site on Saturday and said he had asked President Donald Trump to declare a state of emergency, a technical move that triggers federal assistance in repairing damage. According to a timeline provided by the authorities, police were called to the area to respond to gunfire at 5:30 am, and officers spotted the motorhome at 6:00 am.

Fifteen minutes later, they heard an audio countdown coming from the vehicle warning of a bomb -- interspersed with music -- and the need to evacuate.

Police have not said if anyone was inside the motorhome at the time, but lauded the officers who arrived at the scene and took quick action.

A total of 41 businesses were damaged, Mayor John Cooper said.

Adding to the cryptic nature of Friday's incident was the eerie preamble described by witnesses - a crackle of gunfire followed an apparently computer-generated female voice from the RV reciting a minute-by-minute countdown to an impending bomb blast.

Police scrambled to evacuate nearby homes and buildings and called for a bomb squad, which was still en route to the scene when the RV blew up just outside an AT&T Inc office building where it had been parked.

The explosion occurred about two blocks from Lower Broadway, where some of Nashville's famous live music venues are located. The Ryman Auditorium, former home of the Grand Ole Opry and just three blocks from the blast scene, was undamaged. The Gaylord Opryland and current Grand Ole Opry complexes, which sit outside the downtown area, were not impacted.

The motorhome was parked in front of a building for phone company AT&T, causing damage that disrupted telecommunications service in Tennessee as well as parts of Mississippi, Kentucky, Alabama and Georgia.

AT&T's efforts to restore services overnight were waylaid when a fire reignited at the company's downtown office at the site of the blast, but the company said in a statement on Saturday it was deploying portable cell sites to downtown Nashville and across the region.