NEW DELHI: Panic buttons will have to be fitted on all India's public buses to curb sex attacks on women, the transport minister said Wednesday, more than three years after the fatal gang-rape of a student on a bus in Delhi.

The transport ministry said it would issue a formal order after June 2 making the emergency measures on public buses a must.

“To ensure the safety of women after the unfortunate incident, we have decided to make it mandatory for public transport buses to install emergency panic buttons, CCTV cameras and GPS-enabled vehicle tracking devices,” Nitin Gadkari told reporters in New Delhi.

He was referring to the brutal attack on a woman in December 2012 as she returned home from the cinema.

The assault triggered outrage and mass protests across India, leading to an overhaul of its rape laws but high numbers of assaults persist.

Rajasthan is the first state in India to have such buses, with 20 vehicles fitted with the new safety measures.

Panic buttons are placed above the front doors which, once pressed, send an emergency message to a police control room that can then view live footage of the bus interior.

Gadkari said all public buses would have to be modelled the same way, while manufacturers must ensure new buses come equipped with the facilities.

The government's latest anti-sex attack move follows its announcement last month that all mobile phones sold in India would have to have a panic button from the start of 2017.

The button would allow users to call emergency services by pressing a single key on their phone.