West Sacramento in California has launched a controversial new program that monitors what people are talking about online.

ZenCity trawls through all publicly available posts on Facebook, Twitter and Instagram to find out what people are talking about and whether the opinion they are expressing is positive or negative.

City leaders insist the pilot scheme allows them to quickly respond to issues citizens are complaining about online, but privacy campaigners will worry about the mass harvesting of data following Facebook's Cambridge Analytica scandal.

ZenCity trawls through all publicly available posts on Facebook, Twitter and Instagram to find out what people are talking about and whether it is positive or negative

Mayor Christopher Cabaldon has signed up to the program for the whole of 2018 at a cost of $12,000, a 60 percent discount on the normal rate.

'It allows us to hear the whole community and not just the loudest voices that come to our chambers for a public hearing,' he told CBS 13.

In March, a shooting scare at a local high school led to people complaining about the lack of updates from police, which ZenCity picked up.

The Tel Aviv-based company says policymakers can stay up to date with public opinion on social media in real time through a cell phone app, allowing quick responses to issues.

Mayor Christopher Cabaldon has signed up to the program for the whole of 2018 at a cost of $12,000. Undated file photo

They can also use a geolocation feature to see the views of social media users in specific areas.

But digital rights advocate Peter Eckersley, of the Electronic Frontier Foundation, believes there are 'many ways' the system could go wrong.

'Once you get into policing there are many more potential concerns around the use of artificial intelligence,' he said.

Civil liberties campaigners will point towards Facebook's recent data harvesting scandal as an example of how technology that relies on collecting mass social media data can go wrong.

This saw Facebook data from millions of users transferred without their knowledge to consultancy firm Cambridge Analytica, which then used it to help political groups including the Trump campaign generate personalized adverts.

West Sacramento is the first US city to sign up to ZenCity, although the start-up claims to already have a presence in local authorities around the world, including Paris.

People that wish to opt out of the program can change their social media accounts to private.