Nearly half of Australian households are unable to watch the ABC's 24-hour free-to-air news channel on their television sets.

The taxpayer-funded channel ABC News 24, which launched last night, is being broadcast in high definition (HD), replacing ABC HD, which was previously provided as a simultaneous broadcast of ABC1, a standard definition (SD) channel, on HD.

This means viewers need a HD-compatible set-top box or TV to watch the channel. Pay TV subscribers who have not upgraded to a HD–subscription will also not be able to access it.

According to the latest figures from the federal government's Digital Tracker Report, about 68 per cent of Australian households have converted to digital TV, of which 84 per cent have access to HDTV, meaning only 57 per cent of viewers have HD sets.

News junkies wanting to get a glimpse of the channel can watch it online at abc.net.au/news/abcnews24/ or on iView, but there's a catch.