A Santa hat-clad thief who allegedly stole a wheelchair from a man using a toilet in Federation Square has been charged.

The alleged thief left his victim stranded in the toilet for an hour on Sunday until a passerby came to his aid, police said.

A man has been charged after a wheelchair was stolen and a man was left stranded in a toilet at Federation Square in Melbourne.

Police earlier said the man struck up a conversation with the 54-year-old victim at Flinders Street station about 11am.

The pair went to a toilet at Birrarung Marr, where the offender assisted the man into the cubicle before stealing his electric wheelchair.