Swedish teenager Greta Thunberg said on Friday she doesn't understand why grown-ups and world leaders would mock children and teens for acting on science, responding to attacks on her campaign as students conducted a second wave of global protests demanding action on climate change.

When asked about US President Donald Trump and others who have mocked her, the 16-year-old activist said they likely feel their world view and interests are being threatened by climate activism.

"We've become too loud for people to handle so people want to silence us," she said at a rally in Montreal after meeting Canadian Prime Minister Justin Trudeau. "We should also take that as a compliment."

The youth climate movement has drawn criticism from some who accuse the students of overreacting and say they would be better off going to school.

In an apparent sarcastic jibe at Thunberg this week following her haranguing of world leaders, Trump tweeted: "She seems like a very happy young girl looking forward to a bright and wonderful future. So nice to see!"

Instead of addressing Trump by name, she said Friday that she didn't "understand why grown-ups would choose to mock children and teenagers for just communicating and acting on the science when they could do something good instead."