LOS ANGELES (Reuters) - NBC on Sunday announced more record audiences for its prime-time TV coverage of the London Olympics, even as the Twitterverse erupted in complaints about the U.S. network's online streaming efforts and delays in broadcasting key competitions.

Contributions to the Twitter hashtags #NBCfail and #NBCsucks surged on Sunday, with many posters complaining about the quality of NBCUniversal's online platform, which promised to show every sporting contest live for those unwilling to wait hours for the network's main primetime coverage of the day's events.

"you suck! I can't stream anything because your website is broken. It even verified directtv account, just to tease me. #NBCFail" read a posting to #NBCfail on Sunday by Twitter user Beth Hodgson.

Others complained about the plethora of ads interrupting NBC's coverage across multiple broadcast and cable outlets, and commentary by some of the NBC anchors.

"Finally got @nbcolympics live stream working online only to find it full of ads & streaming issues," Cindy Gallop said on Twitter.

NBC top sports executives were in London and could not be reached for comment on Sunday because of the time difference with the United States. But NBC Olympics producer Jim Bell took to Twitter to respond briefly to some of the gripes early on Sunday.

"Coverage on both net & cables a mix of tape and live events. Yesterday nearly 40 hours of live Oly sports on television btw," Bell tweeted.

TV AUDIENCE SOARS, BEATS ATLANTA, BEIJING GAMES

Despite the grumbling, NBC said on Sunday that a record 28.7 million U.S. viewers watched its primetime coverage on Saturday's first day of competition, when popular swimmer Michael Phelps was shut out of the medals for the first time in years.

NBC said Saturday's evening audience was 2 million more than watched the first day of competition during the Atlanta Olympics in 1996. An average 12.3 million U.S. viewers watched the Olympics on television on Saturday morning - a 56 percent increase over the Saturday daytime audience for Beijing in 2008, the network said.

NBCUniversal, which is majority owned by cable operator Comcast Corp, paid $1.18 billion for the U.S. rights to broadcast the London Games, and has won $1 billion in advertising for its Olympic broadcasts over the next three weeks.

It is planning an unprecedented 5,500 hours of cover across its cable and free-to-air outlets, and its NBCOlympics.com website - more than double the hours devoted to the Beijing Games.

NBC drew a record 40.7 million U.S. television audience for Friday's opening ceremony from London, despite complaints that Americans had to wait for up to seven hours to watch the ceremony.

Those wanting to watch online must have an account with a cable television or satellite provider, or download an app from NBC. According to the Nielsen company, about 90 percent of Americans subscribe to either cable or satellite services.

Not everyone was unhappy with NBC's efforts however.

"I'm watching tons of live events on NBC's Olympics app. I don't understand the #nbcfail nagging. Bonus: No commentary, just game sound!" Twitter user Mtolander posted on Sunday.

Brad Adgate, media analyst for Horizon Media in New York, told Reuters on Sunday: "Whatever NBC does they will receive criticism, especially in the Social Media Olympics, you can't please everyone. TV though remains the big ad revenue producer and they paid 1.18 billion dollars, so what do you expect?"

Adgate said the strong ratings for the London games were surprising, especially for an Olympics outside the United States.

"It's one thing to run ahead of Beijing, but quite another to be running ahead of Atlanta," Adgate said.