text: Homeland Security Secretary Jeh Johnson said his team had been in "constant" contact since the Paris attacks.
  Elsewhere, hundreds are protesting over plans to clear away homeless residents in central San Francisco.
  The Super Bowl is the climax of the American football season, and a crowd of 70,000 is expected for the game.
  The Denver Broncos will be taking on the Carolina Panthers in the biggest National Football League (NFL) game of the year, as part of a landmark Super Bowl 50 - marking half a century of the big game.
  Thousands of police and security officers are expected to be deployed across the San Francisco Bay area, which covers nine different counties. The game will be held in Santa Clara, about 40 miles (64km) south of San Francisco.
  Officials say they are not responding to a specific threat, but have been urging the public to remain vigilant.
  "We are always informed by recent events and what we see in the world situation," Mr Johnson told reporters earlier this week, referring to the deadly attacks in Paris in November last year which killed 130 people.
  "The threat picture is different every February," he added, keeping a tight lid on further details of the security plans.
  A senior NFL official, Jeffrey Miller, told Reuters that some 4,000 private security staff had been brought in to support police in securing the area.
  Meanwhile, CNN reports the US Air Force is deploying two of its aircraft - an F-15 Eagle and a Cessna 182 - to provide air cover for the major sporting event.
  The use of drones from flying within 32 miles of the Super Bowl stadium in Santa Clara, California, has also been banned between 14:00 and 23:59 PST on 7 February.
  In a video to sports fans released on Thursday, the Federal Aviation Administration (FAA) warned the stadium is a "no-drone zone".
  It comes as protests erupted this week over plans by the authorities to clear the streets of San Francisco of its homeless residents.
  Some 200 people gathered in the city on Wednesday shouting "no penalty to poverty", and demanding the authorities do more to help the city's estimated 7,000 homeless people.
  San Francisco Mayor Ed Lee indicated in August last year that they would make efforts to remove them, saying "they're going to have to leave".
  But city officials insist they are offering alternative accommodation for homeless people before telling them to move - a claim protesters deny.
  Another point of contention raised by the demonstrators is the $5m expenditure on the Super Bowl, as well as the millions spent on TV advertisements during the game, which some argue could have gone towards housing hundreds of homeless residents.
target: US officials in California have been seeking security advice from French officials, as the San Francisco area prepares to host the Super Bowl.