The new helpline has been launched to help contain corruption among the police force
Five policemen in India are being investigated for alleged corruption after officials received complaints on a newly-launched helpline number.
Since its launch on 6 August, the helpline has received more than 3,700 WhatsApp messages and 622 calls.
Officials said they had received two video and three audio messages and were investigating the reported incidents.
Correspondents say there have long been allegations of corruption in the Delhi police force - and the rest of India.
Delhi police commissioner BS Bassi last week launched a new helpline number , asking the public to send audio or video messages via the instant messaging service WhatsApp "if any cop seeks a bribe or harasses a person".
Advertisements were taken out in popular Hindi and English newspapers as well as on FM radio channels to make people aware about the new helpline.
The "response from the public has been good", deputy commissioner of police Sindhu Pillai told the BBC.
Ms Pillai is part of the vigilance department which investigates policemen after complaints of bribery, corruption, bad behaviour with complainants and inaction on complaints.
"Most of the messages we have received so far are from people wanting to know about this service, but we have also received some complaints," she said.
"Once we get an audio or video clip, we ask the complainant to come to our office and give a written complaint. We get the recording checked at the forensic science laboratory to make sure its genuine and once the authenticity is established, action is taken against the errant policeman."
Of the five video and audio files received on the helpline, Ms Pillai said her department had initiated action in two cases, involving five policemen, for demanding - and accepting - bribes.
In the first case, a complainant sent a video recording of an assistant sub-inspector receiving a bribe of 400 rupees ($6.5; £3.9) while in the second incident, an audio recording revealed four policemen demanding and accepting bribes from a shopkeeper over a period of a year.
"We have registered cases against the erring police officers under India's Prevention of Corruption Act and action has been initiated against them," Ms Pillai said.
The policemen have been suspended.
WhatsApp is hugely popular in India because it is easy to use and carries no advertisements.
The service is available on Apple, Android and Blackberry platforms and it's very cheap.
The messaging service is used by about 500 million people globally and estimates say nearly a tenth of its users are in India.