The government claims the Hunter Valley gas power plant is needed to keep electricity prices down. Critics say it is a costly political boondoggle.
"It's going to bring with it some 600 new jobs during peak construction there and 1,200 indirect jobs across the state," said Morrison. "Importantly, it's going to keep the pressure down on electricity prices across New South Wales."
Despite protests, Morrison faces little domestic political pressure to change his climate policies. The opposition Labor Party also backs coal mining and coal power plants.
But Australia is coming under increasing international pressure on to follow other developed economies and set a target date for becoming carbon-neutral.
So far Morrison has refused, but diplomatic pressure is building ahead of a major international climate summit in Glasgow later this year.
Friday's protests, which organisers said took place in 50 locations, were the latest in a series of strikes inspired by environmental campaigner Greta Thunberg.
The 18-year-old Swedish activist began campaigning for action on climate change in 2018, spending Fridays sitting outside the Swedish parliament with a sign reading "School Strike for the Climate".
Thunberg tweeted her support for the Australian strikes on Friday. "Huge climate strikes today across Australia," she said. "Soon the rest of the world will join in...