A climate protester has breached security at NSW Parliament, jumping from the public gallery onto the chamber floor during question time in a frightening incident that left MPs stunned.

The man, from climate activist group Rising Tide, leapt over the railing in an attempt to confront Premier Chris Minns about halfway through question time on Tuesday.

WATCH THE VIDEO ABOVE: Climate protester breaches NSW Parliament security

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The brazen security breach sparked fears among some MPs that Macquarie St was under attack.

Labor backbencher David Saliba jumped into action along with other colleagues to help restrain the protester.

“There was a large thump,” he said. “Everyone’s backs were turned. I didn’t know what was happening at that particular point in time. Just knew something was not right.”

The man was detained by Parliament security but was not charged over the incident.

The Speaker has now ordered a full review into the security breach and wider security measures around Parliament House.