Women in a refugee camp in downtown Port-au-Prince: many have been attacked since the earthquake

In one of the great unmentioned effects of the earthquake in Haiti, women and young girls are suffering a rising number of rapes and sexual assaults, according to leading aid agencies. So widespread are the reports - and they include the rape of a girl of 12 by her rescuer after she was pulled out from the rubble - that emergency measures are now being taken.

Displaced men and women patrol some camps with makeshift arms to ward off attackers; girls wear jeans under their skirts for protection if they go out after dark; temporary women-only health centres are being set up; and NGOs try to deliver aid to dangerous neighbourhoods where women are too scared to go out.

Sarah Spence, gender-based violence co-ordinator for International Rescues Committee, who arrived in Port-au-Prince two weeks ago, said: "Violence against women was a problem in Haiti before this crisis. Now, women and girls are dramatically more vulnerable to attack. The humanitarian community focuses on food, water and shelter, understandably, but this is at the sake of protection for women. Criminal gangs have regrouped; security is poor; people are sleeping in the streets, too frightened to go inside or else in crowded, unlit camps. And many women have been left without male protection because their husbands or brothers were killed."

Spence met two women looking for help for their female colleague who had been raped on the street the night before. The victim had been unable to find medical help because many of the health centres that care for victims of sexual attacks were destroyed or badly damaged in the earthquake.

About half an hour outside the capital, the Ti Source camp is home to 3,000 people who came to the hilly ground to escape their flattened homes in the town of Mariani. Scared by reports of rapes in the town below and neighbouring camps, Martine Josil (24) persuaded some of the men in the camp to form a security group.

She said: "After the earthquake we felt very afraid because people were talking about rapes in other camps. There were many women who had lost their husbands and they felt very vulnerable. We didn't want to get raped so we asked the guards to protect us."

The men, and some women, carry makeshift weapons - iron bars and knives - and guard the camp throughout the night.

In Port-au-Prince, two female health centres have been set up by in the past week, providing rape victims with life-saving medical treatment such as retroviral drugs which protect against HIV. More than 5% of the adult population have HIV/Aids in Haiti, the highest rate outside Africa.

Rates of sexual and domestic violence against women and girls in Haiti are among the highest in the world. In the days after the earthquake, a Swiss doctor, Olivier Hagon, told the Swiss newspaper 'Le Temps' that he treated a young girl, no older than 12, for vaginal tears after she had been pulled out from under the rubble and then raped by her rescuer.

Rape was criminalised only in 2005 but it remains shrouded in shame. Victims are often forced out of school and ostracised by their communities. Many victims do not report violence because they have little faith in the criminal justice system.