Two 155-metre chimney stacks have come crashing down as part of a planned demolition at the Munmorah power station on the New South Wales central coast.

The chimneys, once an iconic feature of the southern Lake Macquarie skyline, were stacked with various explosives and fell in just seconds.

Each chimney was made up of 6,500 tonnes of concrete making an enormous impact upon hitting the ground.

The power station was closed five years ago, a move welcomed by environmental groups who had previously referred to Munmorah as one of the state's oldest and dirtiest plants.

The remnants of the chimney stacks. ( ABC News: Emma Simkin )

Today's implosion was part of the clearing of the site but what the land will be used for in the future is not yet known.

Many locals set up at various vantage points around the old plant to watch the demolition, cheering when the chimneys fell.

Stephen Saladine, managing director of Generator Property Management, the owner of the plant, said the blast went according to plan.

"We did a significant amount of planning for this, detailed engineering and it was a textbook drop of the chimneys, very well done to the contractor and [I'm] very pleased to see those safely on the ground," he said.

The plant was opened in 1967 but high maintenance costs of the facility resulted in Delta Electricity closing the site and getting approval for its demolition.