A dutiful Sydney bank worker on a push bike has helped catch a man who police believe is part of an international ATM fraud syndicate.

Police were contacted shortly before 7:00pm (AEDT) on Sunday by the staff member, who had identified a man allegedly making suspicious transactions at a number of ATMs at Haymarket in the inner city.

The worker then got on his bike and rode to the area, with a colleague giving him phone updates on where the transactions were being made.

A Romanian national tried to run away when he was approached by police.

Police say they searched the man and found a large amount of cash and a number of credit and gift cards.

Officers have also found the man was in Australia illegally after his visa expired in May this year.

The 35-year-old has been charged with dealing in the proceeds of crime and 39 counts of possessing a false document.

He has been refused bail to face court today.

Police say they believe the man is part of a syndicate involved in fraudulent transactions across the country.