Sharks have forced the closure of popular beaches to the north and south of Sydney.

Two popular South Coast beaches have been shut after a 17-year-old Sam Smith's arm was apparently mauled by a shark.

His friend said he watched the teen surface, screaming that he had been bitten.

"It started coming for him, so he stabbed it with his spear to try to scare it off, and then it just went ballistic and bit him," Luke Sisinno said.

Lifeguards closed Narrawallee Beach and North Mollymook, after the incident happened around midday.

It's understood Smith was spearfishing before he was bitten.

An ambulance spokesperson has told Yahoo7 that the teen suffered multiple lacerations to his hands and fingers.

He was treated by paramedics at the scene before being taken to Milton Ulladulla Hospital, where he remains in a stable condition.

An ambulance helicopter was sent, and the Westpac Rescue Helicopter conducted sweeps of the area.

Our lifeguards are monitoring the situation and will take further action if required to protect beachgoers, the Australian Lifeguard Service's Brent Manieri said in a statement.

Go here to read the rest:

Shark attack shuts South Coast beaches