MONTREAL (AFP) - Teen activist Greta Thunberg urged Canadian Prime Minister Justin Trudeau and other world leaders on Friday (Sept 27) to do more for the environment as she led half a million protesters in Montreal as part of a global wave of "climate strikes."

The 16-year-old Swede met privately with Trudeau but later told a news conference with local indigenous leaders that he was "not doing enough" to curb greenhouse gases responsible for global warming.

"My message to all the politicians around the world is the same. Just listen and act on the current best available science," she said.

Thunberg generated headlines around the world earlier this week with her viral so-called "How Dare You?" speech at the UN climate summit, accusing world leaders of betraying her generation.

"You have stolen my dreams and my childhood with your empty words," she thundered, visibly angry and close to tears.

The teen has inspired millions of youths, drawn to her cause by her passion and a mature, committed rhetorical style - articulated in near-perfect English - that belies her young age.

Trudeau and other Canadian party leaders took a breather from a tight election campaign to join Thunberg at the Montreal rally - along with around 500,000 protesters, according to organisers.

Walking with his wife and children, Trudeau mingled with a boisterous crowd that brandished placards reading "Respect Mother Earth" and "Make America Greta Again" - a riff on a campaign slogan popularized by US president and noted climate change sceptic Donald Trump.

One man was tackled by security when he appeared to lunge at the prime minister, while 13-year-old Annabelle Vellend broke out in tears when she spotted Thunberg, telling AFP: "I really believe in Greta's movement."

"She is doing amazing things and it's great that she's able to press politicians to act on climate change, during an election," she said.

TWO BILLION TREES

In his first term, Trudeau cast himself as a champion in the fight against global warming, but his green image was tarnished by his nationalisation of an oil pipeline to salvage the construction project after years of delay.

The prime minister said after meeting Thunberg and pledging to fund the planting of two billion trees: "I agree with her entirely. We need to do more."

Earlier this week, the Liberal leader vowed that Canada would reach net-zero carbon dioxide emissions by 2050, joining 66 other countries that have already signed onto the pledge.

Last Friday, more than four million youths - and adults - rallied in "climate strikes" around the world.

Turnout at events a week on was smaller, but still vocal. In Italy hundreds of thousands of young people took to the streets while an estimated 40,000 protested outside New Zealand's parliament.

In Canada, events also attracted huge crowds in the capital Ottawa, in Toronto and in several other cities.

In the heart of the giant Montreal march made up mostly of children and a few adults, Alexanne Lessard stood out in her tree costume.

"I'm here for our future, to show our government that we the majority want to do something and that they can take big steps that will an impact," she said.

Daphnee Choquette said she came out for her baby girl, whom she carried with her.

"It's too late for us (older people), but not for them. We need to bring about change now," she said.

RECORD CO2 EMISSIONS

In the afternoon, Thunberg is set to take aim at airlines' skyrocketing carbon dioxide emissions in a speech outside the UN aviation agency in Montreal, which is holding its annual conference.

Limiting airlines' carbon footprint is one of the main topics to be discussed by the International Civil Aviation Organization's 193 member states at the meeting, which runs to Oct 4.

Air travel accounts for about two percent of global greenhouse gas emissions, according to the ICAO.

Thunberg sailed across the Atlantic for the recent UN climate summit in New York specifically to avoid flying. She then drove to Montreal in an electric car borrowed from former California governor Arnold Schwarzenegger.

The world's top scientists believe the long-term average temperature rise must be limited to 1.5 deg C over pre-industrial levels to prevent runaway warming and catastrophic longer term damage.

But the level of emissions being released into the atmosphere has risen to an all-time high, triggering global weather hazards from heat waves to intense hurricanes and raging wildfires.

The UN estimates that the world needs to increase its current efforts five-fold to contain climate change.

The UN summit in New York sought to reinvigorate the faltering Paris agreement on climate change.