A man and a young boy have escaped with minor injuries after a paragliding accident at Sydney's northern beaches.

The pair crashed their paraglider and became stuck on a cliff face at Narrabeen Park Parade.

Emergency services were called to the accident at Sydney's northern beaches about midday (AEDT).

The man in his 30s was knocked unconscious by the impact of the crash, while the eight-year-old boy suffered a deep gash to his right leg.

An ambulance helicopter and paramedics from the Special Casualty Access Team were sent to work out how to get them to safety.

A specialist paramedic abseiled down the cliff-face to help them and decided the helicopter was not needed.

Paramedics were eventually able to free the pair.

"They were very fortunate because number one, you're slamming into a cliff face," NSW ambulance spokesman Adrian Humphrey said.

"Number two, they could have slid down further and caused further injury because of the loose shale and all the sand on the side of the cliff."