Durham police say so far there's no evidence that the robberies are connected.
Police advise people walking along the trail at Duke Gardens to be vigilant. They say two people reported robberies there late Monday afternoon. Both suspects brandished guns.
It follows a week of armed robberies near Duke's campus and at NCCU.
On Sunday, another person was held up at gunpoint in the 400 block of Formosa Avenue.
Saturday, hammer-wielding robbers threatened two people on Campus Walk Drive and Morreene Road near Duke's campus.
Police are urging students and others to be aware of their surroundings.
If you see someone or something suspicious, call 911.