A surge in day trippers, school children and people working different hours has led to the state government opting to put on more trains on some lines in the afternoon and changing timetables for parts of NSW's rail network.

Under the latest rejig, three extra all-stops trains will run between Bondi Junction and Hurstville in the city's south in the afternoon, doubling services on the Eastern Suburbs and Illawarra Line from Central Station between 3.15pm and 3.45pm.

The extra trains to run from October 17 mean four existing services bound for Cronulla and Waterfall in south Sydney will stop at fewer stations, in an attempt to reduce crowding and trip times by up to eight minutes.

Patronage on Sydney Trains' network is growing at about 8 per cent a year, leading to overcrowding on services during peak hours.