The new Shoreham power station will be fired up for the first time within weeks.

Staff at the £200 million plant are getting ready to start up the new gas turbine on August 21.

It will be the first time the 100m chimney, which dominates Shoreham Harbour skyline, will be put to use.

John Thomson, site manager at the power station, said residents may see vapours furling out of the chimney during one of the first phases of testing.

Shoreham is the fifth gas-powered power station he has built.

He said: "There could be some vapours visible but it depends largely on the weather and the conditions in the power station we are testing.

"It is exciting process from an operational point of view."

Further tests will follow during which large amounts of steam will be clearly visible, billowing from the chimney for about ten days.

A spokesman of South Coast Power, which owns the station, said: "The steam blow, driving steam through all the on-site piping, is necessary to clean, or purge, the system. It will protect the generation equipment from potential damage."

The plumes of smoke could at first be discoloured from rust blown out of the pipes.

In a newsletter to hundreds of nearby homes, South Coast Power has reassured residents there is nothing to worry about.

The spokesman said: "This steam is comprised of ordinary water and will be dispersed by the wind and prevailing weather conditions."

It is hoped that the power station, which will generate enough electricity for about 400,000 homes, will be fully operational and feeding into the National Grid by the end of the year.

Gas, piped in from a storage centre at Devil's Dyke, is already on site.

The spokesman said: "The power system in the South-East is extremely overburdened. This new station will help but we cannot say electricity generated in Sussex will go to homes in Sussex. It feeds into the grid for all homes to use."

Construction work at the power station, the only one in Sussex, started in March last year.

At the height of building work, more than 500 people were employed on the project, on the site of the old Brighton B power station. Now there are fewer than 100 staff from contractors Alstom working in the building.