Extra trains will be run between Sydney and the Blue Mountains to reduce severe overcrowding in carriages on weekends and allay fears some tourists will stop visiting the world-heritage area.

Bowing to pressure from tourism operators and local residents, the state government has announced plans for 24 new express train services between Sydney's Central Station and Katoomba in the Blue Mountains on weekends from late this year.

Some trains to the Blue Mountains have been running at more than 150 per cent capacity at weekends. Credit:Michele Mossop

The express trains will operate eight-carriage sets – double the size of those running at present – and cut the travel times for a return journey by about 20 minutes to four hours.

The increase equates to about 25,000 additional seats each week, including an extra 18,000 on weekends. A new return express service between Lithgow and Sydney will also run on weekdays.