Two of Vincent Van Gogh's most iconic paintings have been reunited for the first time in more than 60 years.

The bright, yellow paintings of sunflowers will hang side-by-side at London's National Gallery.

One painting is already on display in London, the other is on loan from the Van Gogh Museum in Amsterdam.

Only five paintings remain from the 'Sunflowers' series, dating from August and September 1888.

The others are currently residing in Tokyo, Munich and Philadelphia.

Each painting is estimated to be worth about $200 million.

"For many people these pictures start the modern movement in art," art historian Godfrey Barker said.

"They're brilliant in colour. They have flattened perspective.

"They're like no flower paintings anyone had ever seen before.

"They're excited. They're animated. The flowers are fighting each other, talking to each other."

Van Gogh painted the Sunflowers series to decorate a bedroom for fellow artist Paul Gauguin in a house they rented in Arles in southern France.

They were meant as a sign of friendship and welcome.

The pair worked together throughout autumn 1888, but it ended at the end of the year when Van Gogh appeared to have a nervous breakdown, famously cut off part of his ear and entered an asylum.

Van Gogh wrote to his brother Theo while he was painting the now infamous oil on canvas artworks.

"I am hard at it, painting with the enthusiasm of a Marseillais eating bouillabaisse, which won't surprise you when you know that what I'm at is the painting of some sunflowers," he wrote.

"If I carry out this idea there will be a dozen panels. So the whole thing will be a symphony in blue and yellow.

"I am working at it every morning from sunrise on, for the flowers fade so quickly.

"I am now on the fourth picture of sunflowers. This fourth one is a bunch of 14 flowers... it gives a singular effect."

The paintings are expected to draw huge crowds to the London gallery.

The display will also include the results of recent scientific research into the two paintings carried out by both the National Gallery and the Van Gogh Museum.

ABC/BBC