March 18 (UPI) -- Two people were injured after another explosion occurred in Austin, Texas, on Sunday night.
The Austin-Travers County Emergency Medical Service said two males in their 20s suffered serious injuries that were not life-threatening.
Police are still investigating the cause of the explosion and advised that people living within a half-mile radius of the explosion to stay indoors until "at least daylight."
"Not only do not touch any packages or anything that looks like a package," Austin Police Chief Brian Manley said Sunday night. "Do not even go near it at this time because given the darkness, we have not really had an opportunity to look at this blast sight to determine what happened. But it is obvious there has been an explosion and it's obvious it caused significant injuries to two people."
Austin resident Eliza May lives 200 feet from where the explosion occurred and told The New York Times she thought a transformer blew up in her backyard.
"It sounded like when the transformers go out, but it was five times magnified that," May said.
Sunday night's explosion was the fourth this month in Texas' capital city. Two people were killed after three separate bombing incidents on March 2 and twice on March 12. No arrests have yet been made in those incidents.
The latest explosion occurred just hours after Manley held a press conference to announce that the reward for information leading to the arrest of the bombing suspect had been increased to $100,000.
Manley also said he believes the earlier bombings were "meant to send a message."
Both victims who died in the previous bombings were black and the areas affected have majority black and Hispanic populations, leading to speculation that the bombings were racially motivated.
"We don't have any evidence," Manley said. "What we know for certain is: We have three victims that are victims of color, and we have three package bombs that have exploded on the east side of Austin."
Austin resident Stan Malachowski heard Sunday night's explosion and told KXAN-TV he fears the attacks are spreading.
"It's not just an east Austin thing, or north Austin thing, it's now southwest Austin. This is not good," Malachowski said.