The University of Manchester has launched an investigation after about 20 female medical students complained of receiving anonymous phone calls in the middle of the night from male callers who intimidated and sexually harassed them.

The calls have been going on for at least three years, according to Charlotte Buttercase, a final-year medical student and one of those targeted.

Woken in the dead of night, female students have been told they are being watched, or have been asked to perform sexual favours, while in other cases callers have screamed gender-based slurs at them.

Buttercase, 24, described her own experience. “On April 16 I was phoned at 2am from an anonymous, no-caller ID and in a two-minute interaction I was subjected to sexually harassing comments.

“Given I was alone in a dark room at 2am – it was one man speaking and three men laughing – I felt incredibly intimidated, demeaned and belittled by this event.”

Speaking to fellow medical students later, Buttercase discovered 16 calls were made in 22 minutes that night, and she was the fifth woman they had called. Others have since come forward with stories of sexual harassment, in person and via phone calls.

In an open letter to the university’s vice-chancellor, Duncan Ivison, Buttercase called for a formal review of what she described as a “pervasive culture of sexual harassment” in the school of medical sciences.

“If one less young woman feels unsafe in her own home, feels less alone in experiencing these attempts to intimidate and belittle her, then we have succeeded,” she wrote.

One in three female students say they have endured sexual harassment during their time at university or college. A recent survey of undergraduates found that students at England’s leading universities were more than twice as likely to experience sexual harassment than those at “lower tariff” institutions.

The research by the Office for Students, England’s higher education regulator, also uncovered hotspots of sexual harassment and sexual assault or violence against those studying courses requiring high entry grades, such as medicine, dentistry, veterinary sciences or languages.

Responding to the Manchester case, the BMA medical students committee co-chairs, Henry Budden and Elgan Manton-Roseblade, said: “These incidents are appalling and have no place in medical school or education. This deplorable behaviour violates the rights of thousands of medical students to be safe, secure and supported whilst training to become doctors.

“The BMA are committed to working with the students at Manchester leading the campaign and, through them, Manchester medical school, and with national stakeholders to support ongoing efforts to eliminate all forms of sexual violence towards medical students across the country.”

Prof Ashley Blom, the vice-president and dean of the faculty of biology, medicine and health, said the issues raised were “deeply concerning” and would be treated with the “utmost seriousness”.

“No member of our community should ever experience behaviour that makes them feel unsafe, intimidated or harassed,” he said. “Our immediate priority is supporting the students affected. We have launched a formal investigation into the specific allegations raised, and we are also undertaking a wider review of the cultural and systemic issues identified.

“We will continue to take whatever action is necessary to address the issues identified and deliver meaningful, lasting change. We know that our students and colleagues must have confidence that concerns will be listened to, taken seriously and acted upon.”