Everyone gathered in the Superdome for Super Bowl fun, but the fun electrical outage disrupted.

Backup systems kicked in at the New Orleans Superdome and kept the playing field and concourses from going totally dark.

But it is still not clear what caused the initial problem on Sunday.

Mayor Mitch Landrieu called the outage “an unfortunate moment in what has been an otherwise shining Super Bowl week for New Orleans”.

“In the coming days, I expect a full report from all parties involved,” he said.

A joint statement from Entergy, which provides power to the stadium, and Superdome operator SMG shed some light on the chain of events, which apparently started at the spot where Entergy feeds power into the stadium’s lines.

The problem occurred shortly after Beyonce put on a spectacular half-time show that featured extravagant lighting and video effects.

“A piece of equipment that is designed to monitor electrical load sensed an abnormality in the system,” the statement said.

“Once the issue was detected, the sensing equipment operated as designed and opened a breaker, causing power to be partially cut to the Superdome in order to isolate the issue.”

The FBI quickly ruled out terrorism, and the New Orleans Fire Department dismissed reports that a fire might have been the cause.

The 73,000 fans were encouraged to stay in their seats.

Players milled around, while others sat down on the bench and field.

A few of them threw footballs around.

“I didn’t know what was going on,” San Francisco 49ers’ Dashon Goldson said.

“I just tried to keep my legs warmed up.”

The Baltimore Ravens, who eventually won the game by a 34-31 margin, felt the delay turned what looked like a blow-out into a close game.

“It really hurt us. We had lot of momentum,” fullback Vonta Leach said.

“We were rolling. That 35 or 40-minute wait, whatever it was, hurt our momentum as far as what we were trying to do. But we came out on top and that’s all that matters.”

Officials gathered on the field and appeared to be talking to stadium personnel.

Finally, the lights came back on throughout the dome and the game resumed.

“Let’s go!” referee Jerome Boger said to the teams.

The NFL said stadium officials were investigating the cause.

“We sincerely apologise for the incident,” Superdome spokesman Eric Eagan said.

The outage provided a major glitch to what has largely been viewed as a smooth week for New Orleans, which was hosting its first Super Bowl since 2002 and was eager to show off how the city has rebuilt since Hurricane Katrina in 2005.

“My exact words on the way over here were, ‘I hope this goes off without a hitch,’ because the city just looked so good,” said fan Monique Richard.

“They were doing so well, the weather was so good  and everything was kind of falling into place.”

New Orleans was once a regular in the Super Bowl rotation – a status it hopes to regain.

The 38-year-old Superdome has undergone $336m (£214m) in renovations since Katrina when it became a desperate symbol of the city’s suffering during the hurricane.

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