The suspect in the deadly bombings that terrorised Austin, Texas, has blown himself up as authorities were closing in on him, bringing a grisly end to a three-week manhunt.

Key points: Suspected serial Texas bomber dies after he detonates bomb during police chase

Suspected serial Texas bomber dies after he detonates bomb during police chase Police have identified him as a 24-year-old white male

Police have identified him as a 24-year-old white male The death comes after a spate of explosions around Austin, which killed two people

But police warned there could be more bombs out there.

The man behind the attacks was identified as Mark Anthony Conditt, an unemployed 23-year-old who bought bomb-making materials at a home improvement store.

Mark Anthony Conditt detonated a device while he was being chased by police. ( Facebook: Danene Conditt )

His motive remained a mystery, along with whether he acted alone in the five bombings in the Texas capital and suburban San Antonio that killed two people and injured four others.

Police tracked Conditt to a hotel about 32 kilometres north of Austin and were following his vehicle when he pulled to the side of the road and detonated a device, killing himself, Austin police chief Brian Manley told reporters near the scene.

"The suspect is deceased and has significant injuries from a blast that occurred from detonating a bomb inside his vehicle," the police chief said.

Two Austin police officers were approaching the vehicle when the suspect set off his device.

One officer fired at the vehicle and the other sustained a minor injury when the bomb went off, Mr Manley said.

The suspected serial bomber is believed to be behind the four explosions in Austin in recent weeks.

Investigators initially had been looking into whether race was a factor in the parcel bombings, but backed off that theory after white and Hispanic victims were also affected.

Fred Milanowski, an agent with the US Bureau of Alcohol, Tobacco, Firearms and Explosives, said it was "hard to say" if the bombing suspect had acted alone.

Officials work at the scene where the suspect in a spate of explosions detonated another bomb and died. ( AP: Eric Gay )

"What we do know is we believe the same person built each one of these devices," Mr Milanowski, the agent in charge of the Houston division of the ATF, said.

"We are not 100 per cent convinced there's not other devices out there."

Asked if the suspect built bombs before the Austin attacks, Mr Milanowski said: "We know when he bought some of the components. It's hard to say whether he was building along the way."

Investigators had tracked Conditt for a couple of days before closing in at the unidentified hotel in Round Rock, Texas, not far from his home in Pflugerville, Governor Greg Abbott told Fox News.

"We've known for a couple of days who the suspect likely was," Mr Abbott said.

"Law enforcement is at his house in Pflugerville where we are learning whether or not that was the location he was making his bombs."

The Governor added that the suspect is believed to have lived with two roommates, who are not currently considered suspects.

Mr Abbott said the suspect was not a military veteran.

Residents told not to let their guard down

Austin police chief Brian Manley says police are investigating the motive behind the bombings. ( AP: Eric Gay )

Police had urged residents of the area to treat any packages with suspicion during the bombing campaign, and Mr Manley warned residents not to let their guard down yet since investigators were not sure whether the suspect had placed or sent more bombs.

Mayor Steve Adler also told CBS News people should remain vigilant.

"We don't know where the suspect has been the last 24 hours," he said.

The first of the four explosions was caused by a package bomb that detonated at a north-eastern Austin home on March 2, killing 39-year-old black man Anthony Stephan House.

Two other package bombs exploded further south on March 12. The first killed a 17-year-old and wounded his mother, they were both black, and the second injured a 75-year-old Hispanic woman.

Mr Manley said investigators still had no clear idea of what prompted the attacks.

"We do not understand what motivated him to do what he did," Mr Manley said.

"We don't know if he was on his way to deliver another bomb.

"He had one with him and that's what he detonated as we approached."

Officials investigating the site of Sunday's deadly explosion in Austin, Texas. ( AP: Eric Gay )

The fourth blast was a roadside bomb that was triggered by a tripwire — a higher level of sophistication than the previous attacks.

In the first three cases police said the packages did not appear to have gone through the US Postal Service or private carriers like UPS, but were left on doorsteps without a knock or ringing of doorbells.

Police were investigating whether a parcel bombing at a FedEx facility on Tuesday morning (local time) was linked to the four other bombings.

An employee was injured at the facility near San Antonio about 1:00am, while a second unexploded bomb was also found at the same facility.

The homemade bomb was bound for Austin.

Police responded to another explosion in Austin on Tuesday evening (local time) at a Goodwill store in the southern part of the city.

Austin-Travis County Emergency Medical Services tweeted that a man in his 30s was injured but was expected to survive.

It was the sixth explosion in the Austin area since March 2, but police did not believe the latest incident was linked to the other bombings.

Map Map: Texas bombings

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