The 25-year-old Irish woman was among a series of foreign victims insulted and sexually harassed by a group of young men aged 15 to 20 in Tay Ho District, a popular Hanoi hangout.

In 2015, Anna* came to Hanoi for the first time to travel with her family and was charmed by the beauty of the capital.

Two years later, she returned to Vietnam to work as a teacher at an international bilingual school in Hanoi.

Late last year, Anna left her rented house in Dong Da District and moved to live with two British colleagues in more expensive Tay Ho District to be closer to her friends.

"It's quiet here and the area offers beautiful lake views, lots of pedestrian spaces and picnic weekends," she said.

On the night of Feb. 10, she and her friend walked home. It was cold and they wore T-shirts covered with wool coats. At the time the street was deserted.

About 300 meters from her house, Anna suddenly heard a noise approaching from behind.

Five motorbikes, each carrying one or two people, veered passed the couple. One man, shouting insults at them, tried to grope Anna, pushing her backward while a teenager hit her arms and chest with his belt to the sound of laughter from his friends.

Back home, Anna could not sleep, with her friend relating the incident via social media and garnering wide-spread interest from the expat community in Vietnam.

Through discussions, she realized she was not the only victim. On Feb. 22, Anna and four other foreign women, also victims of sexual harassment in the West Lake area, filed complaints to the local police.

"All incidents took place in less than 10 seconds," Anna recalled, saying things had happened so quickly she could not identify anyone.

Following the attacks, some expats created a Facebook group called Hanoi Nightwatch as a platform to report cases of sexual assault and suggest ways in which members could protect themselves. It has over 5,000 members to date.

Last Friday, three teenagers, aged 15-16, admitted to Hanoi police they had sexually harassed foreign women strolling around West Lake after viewing pornographic content online.

Unlike rape, harassment is not a criminal offense in Vietnam, but is often considered an administrative violation under the category "indecent speech and behavior."

Under Vietnam's current law, those under 16 are not liable for criminal responsibility, meaning the group of teenagers could be merely fined from VND100,000 to 300,000 ($4.31 to $12.95).

Anna said that even if perpetrators were teenagers, authorities need to dole out stricter punishment so they would understand "their action may be ebullient, but it hurts people very badly."

Sexual assault targeting foreigners is not uncommon.

In 2016, the expat community was shocked as at least 18 cases of sexual assault in Hanoi were shared on Facebook group "Hanoi Massive." The victims were foreign women who said they had been groped by taxi and xe om (motorbike taxi) drivers; seven others recalled being chased and violently grabbed at by men on motorbikes.

In 2017, police in Hanoi's Tay Ho District arrested a Vietnamese man for harassing European women around the West Lake area, but only slapped him with fine.