Plane passengers were shocked when they saw a huge rocket flying past their window that had been launched by locals at a festival below.

Worried travellers aboard the Boeing 737 were on their way from Ubon Ratchathani province to the capital Bangkok in Thailand when they spotted the projectile piercing through the clouds.

It soared high above the aircraft operated by low-cost carrier Nok Air and could have had devastating consequences if it had struck the fuselage or the engines.

A passenger aboard flight DD325 said he watched anxiously as the rocket flew through the air leaving a trail of smoke at around 3 pm on May 16. They estimated the plane was at around 20,000ft.

He said: 'I suddenly felt quite unsafe. I was worried another rocket could be launched and hit the plane. This one was much too close.'

The homemade rocket made out of PVC pipes and TNT had been launched from Roi Et province as part of an annual festival marking Buddhist Lent and the coming rainy season.

However, the explosive soared thousands of feet into the sky, high above the cloud cover, leaving behind a thin trail of smoke.

Thai aviation officials had previously raised concerns about the rockets disrupting flights during the festival. They have urged organisers to inform them of launch schedules ahead of time so pilots and flight planners can be warned early.

President Sarinee Sangprasit of the Aeronautical Radio of Thailand (Aerothai) said they have lobbied officials for stricter measures to limit the height of rockets, which can reach as high as 20,000ft.

Thailand's Rocket Festival, also known as Bun Bang Fai, is held annually to honour Phaya Thaen, the Buddhist deity of rainmaking, as farmers and villagers pray for rain for a bountiful harvest.

The festival has also been the inspiration for the trending Netflix hit 'The Rocket Angels'.

Locals believe the rockets will reach the clouds and help to stimulate impending monsoon downpours, which last until October or November.

Authorities also hope to pass down the decades-long tradition by organising spectacular shows that will fire the imaginations of younger residents.