Police and FBI officers guard the scene of an explosion in Austin, Texas, US, March 17, 2018. REUTERS/Sergio Flores

AUSTIN: Two package bombs exploded miles apart in the capital city of Texas on Monday, killing a teenager and injuring two women in attacks that Austin police linked to a deadly blast earlier this month.

In all three cases, a package was left at the front of a residence and exploded after an unsuspecting victim picked it up or tried to open it, Austin Police Chief Brian Manley told reporters.

?We are looking at these incidents as being related,? Manley said, adding that federal investigators were among those looking for suspects and a possible motive for the attacks.

All the victims, including a 39-year-old man who died in the March 2 blast, were either African-American or Hispanic, Manley said.

?We cannot rule out that hate crime is at the core of this but we are not saying that that is the cause,? Manley told a news conference.

He warned residents to watch out for boxes left outside their homes and to report anything suspicious to police.

The attacks took place as Austin hosted thousands of out-of-town visitors for its annual South by Southwest festival. London Mayor Sadiq Khan gave the keynote address on Monday afternoon.

The Monday blasts were in homes about 6 kilometres (4 miles) apart in East Austin, a predominantly Hispanic and minority area undergoing gentrification after a surge in the city?s population.

The 17-year-old found a package outside his house in a tree-lined, mixed race residential area and brought it into the kitchen, where it exploded, Manley said. A woman at the home, in her 40s, was taken to an area hospital with injuries that were not thought to be life-threatening.

The victim of the second Monday blast was a woman in a wheelchair who had been watering her grass, said Brandon Rendon, a 27-year-old contractor who lives four houses down from her home in the mainly working-class Hispanic Montopolis area.

?It looked like small terrorism,? said Rendon, who heard a loud bang and was among locals who poured into the street to see what happened.

The March 2 incident, initially investigated as a suspicious death but now considered a homicide, occurred at a house in the city?s wealthy Harris Ridge neighbourhood, about 12 miles northeast of downtown. Police said they had no indication it was related to terrorism.