Los Angeles: Pop star Britney Spears was unexpectedly released on Wednesday from the Los Angeles hospital where she was held for a mental evaluation, prompting celebrity photographers to chase her across the city.

Spears, who was taken to UCLA Medical Centre by ambulance and under police escort a week ago, left the facility quietly.

It was not immediately clear why Spears, who had reportedly been ordered to spend two weeks under evaluation, was released. A hospital spokesman declined comment.