Hundreds of thousands of people across the world are taking to the streets to call for urgent measures to tackle climate change.

Millions of people in 139 countries are expected to take part, with 300,000 in Australia having already started.

Inspired by Swedish climate activist Greta Thunberg, students are leading events from Australia to Iceland that highlight the need to address what they describe as a climate emergency.

People across the world will take time off school or work to join the global event.

Image: More than 200 young people stormed the environment ministry in Bangkok

Image: Greta Thunberg has inspired young people to act to tackle climate change

Miss Thunberg, 16, posted on social media just hours before the sun came up for the first countries in the world to see 20 September.

She wrote: "Soon the sun will rise on Friday the 20th of September 2019. Good luck Australia, The Philippines, Japan and all the Pacific Islands. You go first!"

In the UK, there will be more than 200 events and demonstrations, with tens of thousands of people expected to take part.

These include:

Aberdeen at 11am

Birmingham at 11am

Belfast at midday

Cardiff at 10am

Edinburgh at 11am

Newcastle at 11am

Glasgow 11am

London at 11am

Large turnouts are also expected in cities such as New York, Santiago, Brussels, Paris, Johannesburg and Berlin.

The demonstrations will take different forms, but all aim to promote awareness of climate change and demand political action to curb contributing factors to climate change, namely carbon emissions, organisers said.

For example, in Plettenberg Bay, South Africa, people will dance on the beach in a pledge to protect their natural heritage.

In Istanbul a climate festival, concerts and workshops will be held in a public park.

School kids are suing the US government over climate change.

Protests have already kicked off in some parts of the world, including Australia, New Zealand and Thailand.

School Strike 4 Climate has estimated that around 100,000 people are protesting in Melbourne, while a mass demonstration has also taken place in Sydney.

In Thailand, protesters have already stormed the environment ministry in Bangkok and hosted a 'die-in'.

Image: Climate change protesters in Thailand host a die-in after storming Bankok's environment ministry

Businesses have also got involved in the action, with a Lush store in Singapore announcing it would be closed for the day with a sign on its window reading: "Sorry we are closed due to an emergency: the climate emergency."

The events come ahead of a United Nations climate summit, which starts in New York on 23 September.

Image: A Lush store in Singapore has closed as climate strikes take place

Greta will be among those taking part, having recently sailed to New York from the UK in a zero carbon emissions vessel.

On Wednesday she appeared before a number of congressional committees to speak about climate change.

She submitted a report by the Intergovernmental Panel on Climate Change calling for rapid, unprecedented changes in the way people live to prevent temperatures from rising 1.5C by 2030.

She told the politicians: "I want you to unite behind the science. And then I want you to take action."

Barack Obama fist bumps with Greta Thunberg

It comes as the Climate Action Tracker, which measures government climate action against international pledges to limit global warming, says global temperature rises are likely to exceed 1.5C by 2035 without more action.

Under the Paris climate agreement in 2015, countries vowed to keep temperature rises to "well below" 2C above pre-industrial levels and to keep them to 1.5C to avoid the most dangerous effects.

But the Climate Action Tracker said current policies would see 2C breached by 2053 and temperatures rise by 3.2C by 2100.

Bill Hare, chief executive of Climate Analytics - one of the partners of the Climate Action Network, said: "We're heading to at least twice the warming limit governments agreed four years ago.

"It's time for them to strengthen their Paris Agreement targets, as promised, and rapidly scale up action at home. We are inching forward, at best."