England's Josh Tongue labelled Jonny Bairstow a "hero" for protecting the Lord's pitch after the wicketkeeper man-handled a climate activist during the second Ashes Test on Wednesday.

A pair of Just Stop Oil protesters ran onto the outfield from the Lord's Grandstand just before Stuart Broad bowled the second over of the opening day.

Although the protesters sprinkled the group's trademark orange powder on the grass, they did not reach the pitch itself thanks to Bairstow's swift intervention.

The England star grabbed one of the demonstrators and carried them off the playing surface to cheers from the crowd, while the other invader was apprehended by stewards.

A third demonstrator was tackled before making it onto the outfield.

If the pitch had been covered by the powder, Tongue felt the match would have been significantly interrupted or even cancelled.

"I saw Jonny running after him. If they had put the powder on the wicket, who knows where the game would have been," said pace bowler Tongue.

"Jonny doing what he did, who knows, the game could've been called off (otherwise).

"Bit of a hero to be fair, if he didn't stop him, they could've got on the pitch and done something."

Tongue, playing in only his second Test for England, admitted he would not have been as brave as Bairstow.

"I wouldn't go towards them myself in case they had anything else on them," he said.

Just Stop Oil, which wants an end to new oil and gas exploration in the North Sea, has disrupted a series of sporting events, including the British Formula One Grand Prix and English Premiership rugby union final.

Protesters have tied themselves to goalposts during Premier League football matches and thrown orange powder on the green baize at the World Snooker Championship.

Just Stop Oil also delayed the England team bus taking the side to Lord's for the Test against Ireland earlier this month.

- 'Touchy situation' -
Australia opener David Warner revealed his team had been warned about the potential for a pitch invasion from the activists.

But he didn't expect Bairstow's moment of crowd control because the players had been told not to get involved.

"We had been warned before hand it might happen," Warner said. "We didn't really know what to do. We were told to stand away, not man-handle them like Jonny!"

The burly Bairstow seemed to handle the incident with no fear, but his bold actions could have ended in injury.

In 1982, Australia bowler Terry Alderman damaged his shoulder while tackling a fan who invaded the Perth pitch during an Ashes Test.

"We wanted to protect the wicket, we didn't want it damaged," Warner said. "It is a touchy situation. You don't want to be involved in that, but everything's fine."

After the protest drama, Australia were largely in control, reaching 339-5 at stumps following England's decision to bowl first in overcast conditions.

Two wickets late in the day from off-spinner Joe Root gave England renewed hope.

"We were really unlucky in the first hour, there were a lot of play and misses. They could have been three or four wickets down," said Tongue, who removed both of Australia's openers.

"The two wickets Joe got were crucial. They were scoring at a good rate."

Warner, who made 66 before being bowled by Tongue added: "It was quite challenging, very good bowling conditions. We felt they bowled extremely well with the new ball, swung around a bit.

"We stuck to our game-plan. All in all, I think it was a good day.