The final episode of Breaking Bad drew the cult US television show's biggest ever ratings, but there were also more than 500,000 illegal downloads of the finale with Australia topping the illicit rankings with nearly one in five of copies viewed.

The show, about chemistry teacher turned drug lord Walter White, played by Bryan Cranston, ended its fifth and final season a week after winning the best drama award at the Emmys, television's version of the Oscars.

The finale drew 10.3 million viewers in the US, 3.7 million more than the penultimate show the week before, according to ratings tracker Nielsen cited by industry journal Variety.

While AMC, the cable channel which broadcasts Breaking Bad, will be happy with the ratings, they will be less pleased at the number of people who watched the final episode through illicit means.

The show was illegally downloaded more than half a million times within 12 hours of the first illegal copy appearing online, according to online piracy news website TorrentFreak.

Australia had the biggest number of illegal downloads with 18 per cent, despite the show being screened on pay television.

The US was next on 14.5 per cent, followed by Britain (9.3 per cent), India (5.7 per cent) and Canada (5.1 per cent), TorrentFreak reported.

Australia leads the way in pirating the final episode of Breaking Bad, based on torrent numbers. ( ABC )

"Looking at the list of countries... it's clear that piracy is still rampant, even in countries where people do have the option to watch the show legally," it said.

Twitter comments surged before, during and after the finale, making it the top-ranked Social media buzz generating show of the evening, according to the SocialGuide tracker of social media traffic.

The epic drama triggered three times as many tweets as the next most talked about event, an NFL match between the New England Patriots and Atlanta Falcons.

"I can't even believe that the ratings have increased with each episode - I just think it's wonderful," Breaking Bad creator Vince Gilligan told Entertainment Weekly.

"People have asked me, 'Does it make you want to go on and do a bunch more episodes now?'

"Just the opposite. It makes me think, through quite a bit of good luck being involved, we really did pick the right moment to exit the stage, and I feel even more confident of that now than I did before."

The record TV ratings were less than the biggest season finale of The Walking Dead on 12.4 million, but more than twice the biggest audience for advertising drama Mad Men, which drew 3.5 million for the first show in its fifth series, according to Variety.

The figures pale in comparison with classic TV shows of the past, before the TV and media world became so fragmented in the digital era.

M.A.S.H, for example, scored nearly 106 million viewers for its finale in 1983, while Cheers drew 80.4 million a decade later.

The last episode of Seinfeld was watched by 76.3 million people in 1998.

In the current media landscape, talent shows regularly get much bigger audiences than that of Breaking Bad; The Voice got 14.7 million for its latest series debut.

AFP