Greta Thunberg and three other young climate activists on Thursday launched an appeal to EU leaders to "face up to the climate emergency", in an open letter signed by 150 scientists and a host of celebrities.

In an open letter sent to the 27 heads of state and governments of the EU, who will be meeting for an extraordinary summit in Brussels this Friday and Saturday, Swedish teen Thunberg urged immediate action, including seven "first steps, essential to our chance of avoiding a climate- and ecological disaster."

The activists call for a halt on "all investments in fossil fuel exploration and extraction," and an end to "all fossil fuel subsidies," both "effective immediately." They also called for EU states to advocate to make "ecocide an international crime at the International Criminal Court."

The letter authors said the handling of the COVID-19 crisis shows that climate change "has never once been treated as a crisis, neither from the politicians, media, business, nor finance." Among the more than 3,000 initial signatories from 50 countries are several renowned climate scientists, such as Hans Joachim Schnellnhuber, and Professors Kevin Anderson and Michael Mann.

The call is also backed by a host of international celebrities, including actors Leonardo DiCaprio, Joaquin Phoenix, Russell Crowe, and musicians from British band Coldplay. Thunberg, 17, who has stayed at home in Sweden during the Covid-19 crisis, co-signed the letter with Germany's Luisa Neubauer, 24, Belgium's Anuna de Wever and her compatriot Adelaide Charlier, both 19.

The activists are scheduled to have a videoconference with EU Commission President Ursula von der Leyen, a press officer for the Commission said.