A prominent Perth DJ and community radio presenter has been arrested in San Francisco and charged with kidnapping a two-year-old boy as the child was walking along a street with his mother.

Key points: Roscoe Holyoake has worked as a DJ at Perth clubs and the Sydney Mardi Gras

Roscoe Holyoake has worked as a DJ at Perth clubs and the Sydney Mardi Gras He is accused of snatching the child on one of San Francisco's busiest streets

He is accused of snatching the child on one of San Francisco's busiest streets Bystanders reportedly chased him down before he gave himself up to police

Roscoe Bradley Holyoake, 34, is being held in the county jail on a felony charge of kidnapping, San Francisco Sheriff's office records show, with a $US500,000 ($700,000) bond listed.

Local media are reporting a 32-year-old mother was walking with her child in the Castro District of the city when a man allegedly tried to grab the boy.

The reports said the mother allegedly struggled with Mr Holyoake as he seized her son.

Mr Holyoake then ran off and was chased down by witnesses who held him until police arrived.

Adam and Sabrina Walker were walking with their son when they heard the mother start screaming for help, saying someone had taken her child.

Holyoake has worked as a DJ at a variety of events. ( Facebook: Roscoe Holyoake )

Ms Walker said Mr Holyoake suddenly stopped running, put the child down, smiled at everybody and started sprinting again.

Her husband gave chase for several blocks.

"Without really thinking too much about it, I took off running after him," Mr Walker told abc7 television station in the US.

"Once the man saw that he was kind of cornered he just gave up, put his hands in the air and at that point I went and grabbed him and walked him over to the sidewalk."

Police reportedly said the toddler was injured, but not seriously, and the family had declined medical treatment.

Well-known DJ played at Mardi Gras

Mr Holyoake performs under the moniker DJ Roski and recently played at the Sydney Mardis Gras.

He has worked as a DJ at Connections Nightclub in Perth and recently played at a wrap party for comedian Tim Minchin's new mini-series Upright.

He has been a volunteer presenter at Perth community radio station RTRFM on and off over the past five years.

RTR confirmed he was involved sporadically as a presenter of a weekly show called All Things Queer, discussing LGBTI community issues.

He was also a board member of Pride WA for two years before standing down in February.