NEW YORK: One week into the Olympic Games in Rio de Janeiro it looks as though, despite being in a more favourable time zone, US television viewers are not tuning in to the extent they did for the London Games in 2012.

Across the first five nights, Nielsen data shows NBC averaged 27.9m viewers and a 15.3 household rating, down from 35.1m viewers and a 19.4 rating four years ago.

Viewing figures peaked at 33.4m on Tuesday when the US team was registering a string of successes in swimming and gymnastics, but as Advertising Age noted, that still represented a 13% decline in terms of household rating – from 21.8 to 18.9 – compared to the same evening during the London Games.

As expected, some of the missing viewers have defected to cable and live streaming, which have enabled NBC to cover more events.

"We consciously went into these Olympics with a strategy to put content across all platforms," Mark Lazarus, chairman of the NBC Sports Group, told the New York Times.

"We committed to stream every event live and put Olympic content in prime time on our cable networks for the first time."

But even adding in the 2.3m watching on cable on Tuesday, and the 404,000 streaming live video and earlier events, still leaves NBC short of the 38.8m figure it reached during the equivalent evening in 2012.

Since the network reportedly promised advertisers it would deliver ratings to match or exceed the 17.5 household rating average of the London Games, the Nielsen figures suggest it may have to offer some free commercial time to compensate for the low viewing figures.

But – so far at least – advertisers appear relaxed about the ratings. "Clearly, I'd like the Olympics to be up in prime time, but I'm not worried," said Jack Hollis, group vice president of marketing for Toyota Motor Sales in the US. "As long as we pick up lost viewers elsewhere I'm pleased," he added.

More than 300 brands have bought national ad time across NBC, NBCSN, Bravo, USA Network, CNBC and MSNBC, with the automotive category alone accounting for almost 20% of all Olympics TV spending.

Data sourced from Advertising Age, New York Times; additional content by Warc staff