Thousands of Lawrence residents suddenly found themselves in the dark late Wednesday when their power went out.

About 3,100 customers were affected when a transformer at the power substation went out at Sixth and Kentucky streets near downtown, Westar Energy spokeswoman Karla Olsen said.

6News: Power outage leaves thousands in dark

She was not sure what caused the outage.

The power outage extended west from downtown to Iowa Street and south to Harvard Road. Some areas of Massachusetts Street were without power, including the west side of the 900 block. The outage extended north to about Fourth Street.

Witnesses reported hearing multiple explosions coming from a transformer on a pole near Ninth and Kentucky streets.

“I was standing up on the corner when I heard a pop,” said Danny Miller, of Overland Park. “I looked up and saw a Fourth of July celebration flying everywhere.”

At 11 p.m. Westar crews were in the process of switching customers to other circuits to get their power back on, Olsen said.

Lawrence firefighters blocked an area of Ninth Street near Kentucky because it appeared a power line was about to drop.

During the outage, a group of KU students milled around the area where the transformer blew. Some of them scavenged the area, picking up debris, such as a large spring and another piece that looked liked a small hockey puck.

Several people also gathered near the transformer, throwing out ideas on what caused the explosion and talking about where they were when the outage happened.

KU student Liz Waters said she happened to be in the bathroom of her house in the 800 block of Ohio Street.

“It was pitch black,” she said. “It was pretty scary. I thought if I opened the door, there would be light. But there wasn’t.”

Waters said she had to use her cell phone to see around the house so she could light candles.

Other Lawrence residents had concerns about the outage being a hazard to drivers and pedestrians as traffic lights were out at several intersections.

William Renfro watched as drivers blew through the intersection without pause at Ninth and Vermont.

“Police should be out here,” he said. “This is a big problem. Someone could get hurt.”

Staff writer Joel Mathis and staff photographer Scott McClurg contributed to this report.