Boston Police are investigating several armed robberies and what they are calling “a rash” of parcel thefts in Dorchester’s C-11 district, moving Capt. Tim Connolly, the district commander, to warn residents against leaving packages out in the open or in unlocked cars during the holiday season.

Greater Ashmont Main Streets president Jenn Cartee said in early December that she had been told about three violent armed robberies that had taken place in her district over the last three weeks.

O’Brien’s Market and Deli at 1660 Dorchester Ave. was robbed twice in a two-week period in November, both daytime morning robberies on weekdays, Connolly said. Although the armed robber was alone the first time, he had an accomplice with him when he came back later on.

Connolly said victims described the robbers who took cash as two black men between 18 and 24 years old, who were wearing black clothes and brandishing silver handguns. The store’s owner was in Bangladesh at the time, Cartee said, and “the staff is really shaken.” A married couple tends the store when the owner is away, and the husband was on duty during the robberies. “He was horrified that his wife might have been there for that,” Cartee added.

The boutique Tasha Michelle Kloset, at 1775 Dorchester Ave., was robbed around closing time on Dec. 8 by men matching the profiles of the suspects in earlier robberies. They took about $1,500 worth of cash and cell phones, Cartee said the shopkeeper told her.

Tasha Michelle Kloset’s owner is installing security cameras, said Cartee, who is applying for a $5,000 grant, which she anticipates could cover around 40 high-tech cameras in the main streets district with a 50/50 split between the grant and private funding. The hope is to make the area “less attractive” to potential robbers, she said.

These commercial robberies have taken place at the same time as a series of robberies outside along the Dorchester Avenue corridor, Connolly said. In some cases, criminals appear to be using an app to lure in victims under the pretense of buying or selling a phone, and then stealing the victim’s possessions. Investigations are ongoing in each of these cases, Connolly said, though detectives believe they are narrowing down their search for the armed robbers.

Throughout Dorchester, Connolly said, residents have reported a rash of package thefts. Though there is “no real pattern or specific area,” items left on porches are often at risk for theft around the holidays.

“We prepare for it every year,” Connolly said, and precautions can be taken on all ends of the delivery stage, he noted, adding that if police see a mail carrier delivering a package, “we try to talk to them about putting it out of sight.”

A Dorchester resident shared a scene captured by a video camera doorbell on Dec. 15 showing a man walking up to the porch and taking a very large package. “Perfectly bold and brazen,” Connolly said.

The captain said that this sort of theft is a national problem during the season, and residents should do their best to either have someone home when a package arrives or include specific instructions for a covert place for a driver to leave the item.