Sydney police have established a strike force as they continue to hunt for a man who attacked two young girls in a toilet block in the city's west.

Police say the girls, aged two and six, went with family members to Campbell Hill Pioneer Reserve in Guildford yesterday afternoon.

Officers say the man approached the girls about 1:30pm (AEDT) and took them into the toilets where they were indecently assaulted.

The man fled and emergency services were alerted.

The girls were treated by paramedics.

Police searched the area with the Dog Squad and PolAir, but were unable to locate the man.

Detectives from the State Crime Command's Child Abuse Squad have formed Strike Force Sandyman to investigate the incident.

Sorry, this video has expired Superintendent Peter Yeomans speaks to reporters

The man is described as being of Middle Eastern or Mediterranean appearance and about 165 centimetres tall with a chubby build.

At the time of the attack, he was wearing a black hooded jacket over a dark shirt and blue shorts with white stripes.