The height of a car's tyre, these 50cc petrol-powered machines can hit 50 km/h. Riders are seated awkwardly, with legs apart.

With nowhere to use them, some have taken to riding them at night in deserted places.

On a recent Saturday night, the open-air carpark near Kallang Leisure Park suddenly came alive - with the shrill noise of revved engines.

Four pocket bikes whizzed into view, watched by over 200 people.

At least 50 other similar bikes waited by the sidelines for their turn.

These 20-kg mini bikes cost about $500. While it is not illegal to own them, it is illegal to ride them on public roads.

They are too small, said the Land Transport Authority (LTA).

They are also not allowed in parks, jogging tracks or pavements unless special permission is given by the relevant authority.

And unlike go-karts, there are no dedicated tracks for pocket bike riding here.

Read the full story in tomorrow's edition of The Sunday Times.