(CNN) - Teen activist Greta Thunberg on Friday again criticized world leaders gathered for the COP25 conference in Madrid for not doing enough to stop the ecological crisis that's damaging the planet.
"We have been striking for over a year, and basically nothing has happened," she told activists at the talks. "The climate crisis is still being ignored by those in power, and we cannot go on like this."
The sort of global children's protests Thunberg has inspired and led in recent months are "not sustainable," the 16-year-old continued.
"We cannot go on like that," Thunberg said. "We would love some action from the people in power. ... People are suffering and dying from the climate ecological emergency, and we cannot wait any longer."
She warned that "it is impossible for anyone to know how the world will look in 10 years" and said she hopes the summit will lead to "concrete" change.
"The COP25 is not something we should just look past and ignore. Because every chance we get to improve the situation we must take," Thunberg said ahead of a planned Friday march in the Spanish capital.
Around 25,000 people from 200 countries are expected to attend COP25, the last gathering of the group before 2020, the year the Paris climate accord goes into effect. Attendees include dozens of heads of state and government, business leaders, scientists and activists.
United Nations Secretary General Antonio Guterres said this week that the summit marks the "point of no return" in humanity's fight against climate change. Delegates are expected to try to ink a deal on emissions trading, which experts say could reduce greenhouse gases in line with critical targets set to avert disastrous and irreversible damage.
Thunberg earlier had been mobbed by activists and reporters as she arrived in Madrid by train from Lisbon. Thunberg arrived in Lisbon after nearly three weeks at sea, after two Australian vloggers offered her a ride from the United States on their catamaran, La Vagabonde.
She had already traveled halfway to Chile when the United Nations changed the location of COP25 to Madrid. The South American nation withdrew as host because after weeks of protests paralyzed the country.
Thunberg refuses to fly because of the high levels of emissions emitted in air travel and instead uses boats, trains and electric cars.
CNN's Sharon Braithwaite contributed reporting.