This is the dramatic moment a surprise marriage proposal went wrong when a girlfriend slipped into a mountain stream.

Karantee Areepong, 24, recording a series of moments with his long-term partner Kanyarat Chumjeen, 25, to document their trip to Phrom Lok Waterfall before he proposed in Nakhon Si Thammarat, Thailand.

Footage shows Karantee holding a small artificial flowerpot with a message written on a small paper saying 'Will you marry me?'

He can be seen recording Kanyarat sleeping inside the car, walking in a mall, fixing her hair, and walking near the streams while holding the mini flowerpot.

When the couple reached the waterfall, the unsuspecting woman can be seen carefully stepping on a rock on December 8.

Karantee then called her, prompting his lover to turn around and lose balance, slipping and falling into the water.

The frantic man then jumped into the water, still holding his phone and the flowerpot, to save the bride-to-be.

The girlfriend quickly clung to a rock while still holding her drink and her bag.

The lad managed to grab hold of Kanyarat, and after recovering from the fall, the pair can be heard giggling.

Kanyarat, who was worried about her lover's phone, can be heard saying: 'Phone! Phone! Why did you bring the phone down!'

The boyfriend asked: 'I don't know, I was shocked, Baby. Baby, are you hurt?'

However, the girlfriend asked him back: 'What did you say? What did you say a moment ago?'

He suddenly turned the camera around and said: 'Will you marry me?'

Shocked by the question, she asked him: 'Why did you not choose a better place?'

Moments later, Kanyarat then said yes to the marriage proposal, with them laughing and kissing together.

Karantee said: 'We have been together for nine years, and I have been planning the proposal since September. We met each other while we were studying at secondary level, and since then our feelings developed and we started dating.'