There was only one knock at the door before police officers entered Tanveer Sheikh’s home. Armed men climbed through the windows and began searching room to room, asking for Tanveer.

“We have young girls at home and they were woken from sleep,” said Maryam, Tanveer’s mother. “I told the policemen, how could they barge in like this? We could have been naked.”

Tanveer, who is 16 or 17 years old, according to the family, was not at home in Srinagar, in Indian-administered Kashmir, at the time, so officers took his uncle Naseer instead. The police did not explain why they wanted to detain Tanveer.

“They said: ‘You hand over Tanveer and we will let Naseer go,’” said Maryam.

Naseer’s son keeps asking for his father, who has been held for 11 days. “He is two years old,” Maryam said. “What will we tell him? He will not even understand what has happened.” Naseer is among thousands of people reportedly detained by police as part of a major crackdown launched after the Indian government revoked the region’s special status three week’s ago.

Prominent politicians, including former chief ministers, are understood to be among the detained, as well as business owners and lawyers. Most of those arrested are young men.

According to local media reports, some prisoners have been flown out of Kashmir to prisons in Lucknow, Bareilly and Agra. It is possible that people are being held under the Public Safety Act, a controversial law that allows authorities to imprison someone for up to two years without charge or trial.

UN human rights experts said last week they were “deeply concerned’” by the developments. Groups including Amnesty International and Human Rights Watch have also expressed alarm.

A communications blackout, which has lasted more than three weeks, has severely hampered work by activists to document potential human rights abuses. The suspension of phone and internet services has also left relatives unable to call one another.

The revocation of Kashmir’s special status has stripped it of any autonomy, removing its constitution and rules that have prevented outsiders from buying land. Many Kashmiris fear the change will alter the demographic and traditions of the territory, India’s only Muslim-majority state.

Despite heavy security, sporadic protests have continued over the past two weeks. A sympathiser of a banned political group, who asked not to be named, told the Guardian last week the region was a “burning volcano” that would “erupt any time”.

Delhi’s actions have also escalated tensions with Pakistan, which claims Kashmir and has suggested India could carry out ethnic cleansing.

Outside Srinagar’s central jail, families from across Kashmir queued to visit their loved ones. Aamina said her 22-year-old son, Junaid Nabi Wani, was arrested after Friday prayers two weeks ago.

“He was sitting on the roadside with neighbours and relatives when police came and asked for his identity card,” Aamina said. A police officer then placed his arm around Wani’s shoulder and asked him to take a walk. An armoured vehicle was waiting, she said, and he was bundled into it and taken away. It is not known why he was detained.

“His cousin was with him and he came running to us. We rushed outside and tried to resist but the policemen cocked their guns and pointed them at us,” said Aamina. She was assigned the number 56 by prison staff and asked to wait for her chance to enter the jail. She carried a small lunch box with food for her son.

Sarwar left her home in north Kashmir’s Hathlong village at dawn in the hope of visiting her son, Aqib. She said he was detained in a midnight raid eight days ago. She said no reason was provided for his arrest.

“May God’s wrath fall on them! My son was innocent, trust me he has done nothing,” she said. Her neighbour, Fareeda, had also travelled to meet her son, Bilal, who was detained along with Aqib.

Families waited for hours to see their relatives. “He said nothing. He only cried,” Fareeda said afterwards, breaking into tears. On her arm, a stamp read “ostrich” and “crocodile” – a code that is changed daily that allows entry into the jail.

According to estimates collected separately by agencies, between 2,300 and 4,000 people have been detained. Officials said recently there had been “a few” detentions, to prevent disorder.

Amnesty International accused the Indian government of “deliberate silencing of voices in the region”.

Naseer’s family say he is being held to ransom until his nephew is handed over. Such arrests are common, according to several families in Srinagar’s old city, traditionally a flashpoint for anti-India protests.

A family in the Gojwara locality said police raided their home at midnight on 8 August and asked for their 25-year-old son.

“He was not at home, so they detained his father. He is 70 years old,” the family said. They asked to remain anonymous because their daughters had not been informed.

“When they [daughters] come, we tell them their father has gone out for a walk. When some time passes, we tell them to leave and go home early,” a family member said. “The police ask us to bring our son and take the father back,” they added.

Amnesty International India has previously documented cases where fathers were asked to bring another son for detention if they wanted their first son to be released. “These detentions are not just unlawful but also lead to harassment and intimidation of the families,” said Mrinal Sharma, a policy adviser for the rights group.

Meenakshi Ganguly, the south Asia director at Human Rights Watch, said detainees must be allowed access to proper legal counsel and families should be told where relatives were being held. “International law prohibits indefinite detentions and all those in custody should be swiftly released or charged,” she said.

Aamina said she was scared to be at home and had barely slept since her son was taken. “I promise if he is released I will leave this place. I will beg but I will go somewhere where no one knows us,” she said.

Her husband died last year and her other son has spent two years in prison. “I am all alone now,” she said. “A storm has hit my life.”