AUSTIN (CBSDFW.COM/AP) – Two people were injured in another explosion in Austin Sunday night, and police are not ruling out a connection to the three previous explosions that detonated earlier this month elsewhere in the city.

The latest blast occurred around 8:30 p.m. in a suburban neighborhood known as Travis Country in southwest Austin — far from the previous three that were all in residential areas in the eastern part of the city — and investigators didn’t immediately confirm what caused it. But police Chief Brian Manley repeated previously issued warnings for residents not to touch any unexpected packages left at their homes.

“What we have right now is a scene where it is obvious that an explosion has taken place,” Manley said at a hastily organized news conference near the site of the latest blast.

CBS News correspondent Omar Villafranca told CBS11 that the neighborhood where the explosion took place is under a “virtual lockdown,” with police not letting anyone in or out, at least until sometime Monday morning, while they investigate. He said residents are nervous and understandably in shock.

It was just before 9:00 p.m. Sunday when Austin-Travis County EMS tweeted that crews had responded to reports of explosions in the 4700 block of Eagle Feather Drive and in the 4800 block of Dawn Song Drive.

Manley, responding to reports that the latest explosion may have been detonated by a trip wire, said it was a possibility that the device was “activated by someone either handling, kicking or coming into contact with a trip wire that activated the device.”

He urged people within half a mile to stay in their homes and said authorities would keep the surrounding area blocked off at least until daybreak Monday “given the darkness and size of the area that we want to go in and check.”

“We want to put out the message that we’ve been putting out and that is, not only do not touch any packages or anything that looks like a package, do not even go near it at this time,” Manley said. Because “we have not had an opportunity to look at this blast site to really determine what has happened.”

Manley also said authorities were still working to “clear” a suspicious backpack found in the area that was part of a separate report.

“It is important right now for anyone in the neighborhood behind us to remain inside and give us time to work through this,” he said, adding that any witnesses should call 911 and report what they saw.

Two men in their 20s were hurt in the latest blast. Police said they were hospitalized with injuries that weren’t life-threatening. It was the fourth explosion to rock Austin in less than three weeks.

Earlier Sunday afternoon Austin police had pleaded for help in the case. At an afternoon press conference Chief Manley had made a public appeal for the bomber/bombers responsible to contact authorities so investigators could learn the exact “message” behind the attacks.

It was at that press conference that police also announced an increase in the reward, for information leading to the arrest of whoever is responsible for three earlier explosions that killed two people and injured two others, to a total of $115,000.

The first was a package bomb that exploded at a northeast Austin home on March 2, killing a 39-year-old man. Two more package bombs then exploded farther south on March 12, killing a 17-year-old, wounding his mother and injuring a 75-year-old woman.

Police said all three of those were likely related and involved packages that had not been mailed or delivered by private carrier but left overnight on doorsteps.

According to Manley more than 500 officers, including federal agents, have conducted 236 interviews and followed up on some 435 leads.

On Sunday, police blocked entrances to the neighborhood where the latest blast occurred and put up yellow tape about half a mile from the home where it happened.

Despite the order for those living nearby to stay in their homes, neighbors milled around just outside the tape. Some reported hearing loud booms but couldn’t provide many details. FBI agents arrived to conduct interviews.

Sunday was also the final day of the South By Southwest Music Festival, which draws hundreds of thousands to Austin every March. It is also the end of spring break for many area school districts, meaning families who were out of town in recent days are returning to a city increasingly on edge.

The explosions occurred far from the main South By Southwest activities, though a downtown concert by hip-hop band The Roots was canceled Saturday night after a bomb threat. Authorities later arrested a 26-year-old man, and the incident did not appear to be related to any previous explosions.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)