Operator BAA says Heathrow airport is "jam-packed"
A suggestion by London's Mayor that an airport could be built on an artificial island in the Thames estuary has been branded a "big bad idea".
Boris Johnson wants to look at the feasibility of a 24-hour, four runway airport near the Isle of Sheppey.
Paul Carter the Tory leader of Kent County Council said the estuary was an "unsuitable" location.
But one of Kent's business leaders said a new airport would have huge benefits for the area.
Officials in London are looking at plans to reduce air traffic congestion at Heathrow.
The airport handles more than 500,000 take-offs and landings a year.
At the weekend Mr Johnson said he was looking at the feasibility of a new site somewhere near the Isle of Sheppey.
Councillor Paul Carter said: "Well I'm not best pleased. All new administrations have big ideas and I think this is a big bad idea.
"I think it's a totally unsuitable place for an airport when you think about the winter weather that we have in the Thames Estuary - a lot of mist and fog."
The suggestion has also been criticised by environmental groups who say an airport would have a detrimental impact on wildlife.
However, Mike Lazenby, chief executive of Kent Reliance Building Society said he welcomed Boris Johnson's idea.
He added: "There will always be people that say it is not a good idea but the fact is there are huge benefits to having an airport in Kent.
"The fact is that the road infrastructure and the rail infrastructure in Kent is better than just about anywhere else in the country.
"This would be significant for all businesses in Kent, not just for employment but for jobs and for peripheral business that can all work together to make Kent the right place to have a new airport."
The government is due to make a decision on the proposed expansion of Heathrow by the end of the year.
Operator BAA has been stressing the need for expansion saying that Heathrow is "jam-packed" and needs a third runway to remain competitive globally.
But environmentalists, residents groups and councils opposing the move say the proposed expansion would have a serious impact on hundreds of thousands of homes in the area in terms of air quality and noise levels.