The primary suspect is a 32-year-old woman named Tanya Pagan.
"We're contacting different areas where she could possibly be, and really make it an effort to get her off the streets so she doesn't hurt somebody else," Reading Police Inspector Francis Drexler said.
In the first robbery, Pagan is accused of threatening the clerk at the La Hacienda Convenience Store with what she said was a gun wrapped in a towel.
The second robbery occurred a few blocks away from there at the El Gallito Bakery.
Store Manager Angelica Frutos says the bandit walked in looking like customer.
But when she saw the clerk was alone, she went behind the counter, put her arm around the clerk's neck and held the knife by her face.
The thief was trying to escape with the cash when she ran into one of the bakery workers, who she attacked with the knife.
The bakery worker was hospitalized with a severe laceration.
Frutos says he's doing well, but is still terribly shaken by what happened.
Meantime, local authorities are looking for help from the public, with the warning that Pagan should be considered armed and dangerous.
"We were lucky we have some good witnesses and were able to get her identified fairly quickly, and now we have to do everything we can to get her off the streets," Drexler said.
Anyone with information is asked to call the Reading police at 610-655-6246.
