People stunned after seeing how underwater ship scenes in Titanic were actually filmed

People have been left seriously impressed after seeing how they filmed the underwater ship scenes in Titanic.

The 1997 movie is considered one of the greatest films of all times, and considering it's almost 30 years old, the cinematic effects are seriously impressive.

But have you ever wondered how the underwater scenes were actually executed?

The sinking of the Titanic in the movie is a pretty impressive spectacle - especially when you know how director James Cameron and the rest of the team pulled it off.

There are a number of scenes which recreate the sinking, including Rose and Jack (Kate Winslet and Leonardo DiCaprio) sprinting through the ship while being chased by Rose's ex-fiancé, Cal Hockley (Billy Zane).

Then there's the edge-of-the-seat scene in which the couple are trying to escape the flooded 'third class' cabins after Jack is locked up.

And let us not forget the horrific moment in which the dining room and grand staircase are flooded after water blasts through the glass windows.

So how did they do it?

How were the underwater scenes created? (20th Century Fox)

To create the scenes, a life-size, 775ft replica of the ship was built but split into different sections.

This allowed the production team to essentially tilt different sections of the ship at different times to create the illusion that it really was sinking.

For example, most of us remember the scene towards the end of the movie where Rose and Jack are hanging on to the stern of the ship as it sinks a full 90 degrees.

In one behind the scenes clip of the filming, shared on YouTube page, X-MarcosNavigator, the set could be seen being 'lowered' into water to make it look as though water was flooding in.

Meanwhile, pumps blasting water into miniature sets were also used to create the mindblowing effects.

In one scene, Rose and Jack are running through the sinking ship (20th Century Fox)

Having built an entire replica of the ship, one thing Cameron hadn't necessarily thought of was the lighting that would need to come with it.

"It wasn't just building the set," said the Terminator director. "It was building all the stuff to shoot and light the set that was adding a layer to it that we hadn't really anticipated.

"All the normal Hollywood lighting tools and photography tools went out the window.

"So I thought, 'what about a crane?' The big construction crane on a mobile transporter essentially. So we can move the crane up and down the full length of the set."

Another job was recreating the scene after the ship had sunk, which saw hundreds of people freezing to death in the Atlantic Ocean.

Extras had wax added to their hair to make it look like ice, before having their faces covered in spirit gum and gelatin crystals to simulate frozen faces.

According to Titanic extra, Ellen Mower, the crystals expanded when they got wet or had mist sprayed on them, creating the striking look we saw in the movie.