Man nabbed after NSW parliament evacuated

A man has been arrested after allegedly leaving a suspicious package near NSW Parliament House, prompting a mass evacuation.

Hundreds of workers stood in The Domain for almost half an hour after the alarm sounded on Monday morning.

Police confirmed a suspicious item was found on a walkway between Parliament House and the State Library just before 10am.

A man, believed to be in his 30s, was arrested just after 11.30am on Hospital Road behind parliament, police say.

He has been taken to the Sydney City Police Station and is assisting officers with inquiries.

According to the ABC, police identified the man from CCTV footage that showed someone leaving a suspicious item in the area.

Workers told AAP they were evacuated due to a "security issue" and were simply following procedure.

Among them were about 45 students from St Mark's College in Sydney's northwest who were on an excursion.

Officers guarded either side of parliament's back gate, checking all passes before allowing staff back inside.