This is the excruciating moment a priceless clock falls from a museum wall and smashes into pieces after a curious visitor touches it and knocks it off its hook.

The CCTV footage was posted online by employees at the National Watch and Clock Museum, in Columbia, Pennsylvania, where the incident took place.

Written alongside the clip is the warning: 'This is why we beg and plead with our visitors to please refrain from touching objects in museums.'

The video shows a couple admiring a unique clock hanging up in one of the rooms of the horology museum

The man takes a photograph of the clock before walking towards it to get a closer look and touching it

The video shows a couple admiring the clocks in one of the rooms of the horology museum, which is recognised as the largest and most comprehensive in North America, according to its website.

The man takes a photograph of a rather unique clock - a sculptural piece made by artist James Borden - before walking towards it to get a closer look.

He immediately reaches out with his hand and pulls on the pendulum to make the clock rock from side to side.

Meanwhile his wife, who had also reached out to touch the clock when the couple first walked over to it, takes a step backwards to watch.

The man continues to pull on the pendulum and appears more than confident that it will stay attached to the wall.

Seconds later disaster strikes however as a small part of the clock comes lose and falls to the ground.

The man pulls on the pendulum, which causes a small part of the clock to come lose and fall to the ground

The momentum of the small part of the clock falling causes the entire object to unhook and tumble to the floor

The man tries in vain to stop the clock's descent as his wife looks on in horror as it crashes to the ground

The momentum causes the entire clock to fall from its hook and tumble to the floor as the man tries in vain to stop its descent.

He manages to catch the main body of the clock but many of its smaller parts had already come lose and are seen bouncing off the floor.

Without skipping a beat the man then sets about trying to reattach it to the wall, as if he would be able to do so without drawing any attention to himself.

Meanwhile his wife sets about collecting the little bits of clock from the ground.

After a failed attempt the man realises that the clock is heavier and bigger than he thought and extremely awkward to hold.

He abandons his efforts and instead dumps the clock on the ground before quickly leaving the area with his wife as if nothing happened.

The man manages to catch the main body of the clock but many of its smaller parts bounce off the floor

The man sets about trying to reattach the clock to the wall, as if he would be able to do so without drawing any attention to himself