The number of people visiting Manchester city centre fell by 15.5% in April and 11.6% in May according to the latest figures published by CityCo, the council's management company.
The decline is recorded in the latest Quarterly Economic Outlook published last week by the Association of Greater Manchester Authorities.
CityCo later blamed the fall on problems with the position of one of the four cameras used to record footfall numbers.
A spokeswoman for CityCo said: "While we are aware of a real dip in footfall and sales during March and April, the size of the footfall dip in these figures is a technical issue, due to re-routing of pedestrian traffic in the city after the closure of the Cross Street bridge, which unduly affected one of our footfall cameras. Our understanding is that May and June have been very good months in terms of retail sales in the city, with many double digit year-on-year increases being recorded."
The falling visitor numbers contrast with rising hotel occupancy, according to the same report: "On an annual basis, hotel occupancy rates have increased from 76.6% in May 2010 to reach to 78.1% in the city centre in May 2011.
"Average weekend occupancy rates in the city centre increased to 87.0% in May 2011, compared to 85.0% 12 months earlier. The weekday average in the city centre also grew over the year and was 75.0% in May."
The forecast continued: "Passenger numbers at Manchester Airport stood at 1.4 million in April 2011, equating to a significant annual increase of more than 352,000 passengers compared to the April 2010 figure. Passenger numbers at the Airport now stand at their highest level since October last year, when they were 1.6 million. Moreover, the increase in numbers of 224,000 recorded between March 2011 and April 2011 since May/June 2010. Indications for May are that passenger numbers will be in excess of 1.7 million.
"With passenger numbers having fallen at Manchester Airport over the last two years as a result of the recession, the positive growth between March and April gives cause for optimism."