Lewis Hamilton and Sebastian Vettel have criticised Pirelli’s new-spec 2021 tyres after all teams and drivers ran the rubber during Friday practice in Bahrain.

Following a prototype test in Portugal last month, all competitors were given sets of the revised tyre construction for next season across both sessions at the Sakhir circuit.

Hamilton, who topped Friday’s running, said the new tyres were a “worry” and suggested Formula 1 should stick with running the 2019 tyres into next season.

“Oh god… I’m trying my hardest not to say anything,” the Mercedes driver said after he was asked for his opinion on the 2021 tyres.

“I have the utmost respect for the (Pirelli) guys that come here and load our tyres up, bring them here, and keep us safe. And they do an amazing job.

“We’ve had the same tyre for the last two years. At the end of 2019 they brought a new tyre, which they normally do. And it was quite a bit worse. So then they just said, ‘Okay, well now we just keep the tyre that we had from last year’.

“So they’ve had two years now to develop a better tyre. And we’ve arrived with a tyre that’s three kilos heavier. And it’s like a second worse per lap.

“If you’re going back after two years of development, I mean, I don’t know what’s happening. So it definitely doesn’t feel good out there. And it’s a worry.

“I prefer to just stay on these tyres. If that’s all they’ve got, and that’s the best they can do, which it clearly is, we’d be better just to stay with this tyre.”

Ferrari’s Vettel echoed Hamilton’s comments, saying the new construction was “not a step forward”.

“Probably worth a shot but I hope we don’t see these tyres again. They’re probably quite a lot worse compared to the tyres we currently run,” the German said.

“If (sticking with the current tyres) is the only option for 2021, then absolutely, I would love to stick with the 2019 tyres.

“I think as long as we don’t have a tyre that gives us anything that the current one doesn’t give, such as less overheating, better chance to fight each other, we shouldn’t get onto a different tyre.

“This one is worse, for sure, and it will make all the problems that we struggle with already only worse.”

Free Practice 3 for the Bahrain Grand Prix will commence at 22:00 AEDT on Saturday ahead of qualifying at 01:00 Sunday.