JAKARTA, Indonesia (NYTIMES) - Tunggal Pawestri says she will never forget being groped on a public bus while travelling to her high school in Jakarta, the Indonesian capital, when she was 14.

While Tunggal had become used to enduring daily harassment on her way to and from classes - mostly catcalls and sexually suggestive looks and comments - when a man suddenly began gyrating against her from behind, she said, "I froze."

"I didn't know what to do - I didn't even know that I should have screamed," said Tunggal, who now works for a women's organisation.

Two decades after that disturbing episode, a growing number of activist groups and volunteers like Tunggal are emerging to explain exactly what to do: expose the long-standing problem of harassment on roads, sidewalks, trains and buses across Indonesia, the world's fourth-most populous nation.

"It's an epidemic, and, unfortunately, at the moment, Indonesia has no legal protection for sexual harassment," said Yuniyanti Chuzaifah, vice-chairwoman of the National Commission on Violence Against Women, who said she was once groped after falling asleep on a public bus.

"Women have to be brave to report it, and the police services here are not friendly toward victims," she said. "There's a lot of victim-blaming, like it is their own fault."

According to the women's commission, only 268 street harassment reports were filed last year with the police, nongovernmental organisations or the commission itself across a nation of more than 260 million people.

By comparison, more than 200 women in the Jakarta region alone posted accounts in the past 12 months, both under their name and anonymously, of harassment or groping on the streets or on public transportation to the Indonesia website of Hollaback, an international initiative against street harassment.

"I feel street harassment has been normalised within our society," said Anindya Restuviani, coordinator of Feminist Festival Indonesia, which organises events on women's issues, including harassment.

Activists in Indonesia estimate that millions of street harassment incidents go unreported each year.

"We are sure this is just the tip of the iceberg," said Angie Kilbane, an American high school teacher in Jakarta and leader of Hollaback's Jakarta chapter, referring to the hundreds of posts on the site.

The Indonesian National Police did not reply to multiple requests for official data on street harassment cases.

To discourage sex abuse in public places, the authorities have set aside women-only cars on packed commuter trains and spaces designated for females on public buses, but activists say much more needs to be done - by the government and society.

Kilbane, who has lived in Indonesia for nearly 10 years, said she got involved in combating harassment after a motorcyclist drove up beside her while she was bicycling, grabbed her right breast and said, "Hey, baby," in Indonesian before roaring off.

Kilbane's chapter organises discussions and workshops on sexual harassment and conducts training in self-defence and bystander intervention.

Still, she said, "I don't ride my bike to work any more."

A 19-year-old student at the University of Indonesia, who asked not to be named because she feared publicly confronting her attacker, had anonymously posted two stories of harassment on the Hollaback Jakarta website, one about being molested twice by a close family friend while she was in elementary school and the other about recent catcalling on the street.

Although she said she wanted to share her stories with the group, she has never told her parents what happened and has yet to warn her younger sister, 14, about the problem. She said the issue was considered taboo in Indonesia, and she did not have the courage to tell them.

In 2014, Kate Walton, an Australian activist and writer based in Jakarta, started an online discussion group after experiencing near-daily street harassment. She also has been groped.

In January, she conducted an experiment to gauge the scale of the problem by walking from her home in South Jakarta to a shopping mall 4km away. She was harassed 13 times in 35 minutes and posted a tweet about each incident as it happened.

Walton's discussion group has more than 2,000 Indonesian and expatriate members, and stories of street harassment are a regular topic of conversation.

"The more stories people see, the more brave and willing they are to come forward," she said, expressing frustration at what women in Indonesia endure in public spaces. "It just adds up when it happens every day. It's tiring."

A 2014 report by the Thomson Reuters Foundation found that Jakarta had the fifth-most dangerous public transportation system for women in the world, and the second-worst in Asia behind New Delhi.

Wulan Danoekoesoemo, a clinical psychologist and co-founder of Lentera Sintas Indonesia, which counsels sexual violence victims, said the country's street harassment problem stemmed from its patriarchal society, in which men traditionally hold authority over women.

Adolescent boys, activists said, harass women on Indonesian streets nearly as frequently as men.

"People look up to their peers who catcall or talk inappropriately to women, and it goes without consequences," said Wulan, whose organisation has countered by conducting an education campaign at 78 schools in Jakarta, hoping to change the next generation.

"It's something so common. And for boys, it's one way to prove you are macho and that you are good at pickup lines, which of course they are not," she said.