Another two on-demand bus trials in Sydney will end next week amid warnings from the pricing regulator that the Uber-style services need to be carefully designed to ensure they do not become expensive replacements for existing public transport.

After starting about 18 months ago, a trial at Manly operated by Transdev, and another run by Hillsbus at Carlingford in the city's north west, will cease from May 24. Late last year trials at Punchbowl and Wetherill Park in Sydney's west also ended.

However, four on-demand pilot areas – on the northern beaches, the eastern suburbs, at Newcastle and Woy Woy on the Central Coast – have been extended for six months. Four others, including one at Macquarie Park in Sydney's north, also remain in operation.

An on-demand bus in Sydney's inner west. Credit:Louise Kennerley

The trials, which include those in regional areas, are subsidised by the NSW government to the tune of $20 million, resulting in the cost of a standard adult fare in greater Sydney ranging from $2.60 to $5.60.