No one is close to Mercedes F1 team says Williams's Valtteri Bottas

Bottas's words echo Williams team-mate Felipe Massa's suggestion last week Mercedes' reliability after racking up a mammoth amount of laps was "a big warning" to the rest of F1.

Nico Rosberg set the fastest time on day one of the second Barcelona test on soft tyres, with his time 1.5 seconds quicker than the next best to date on the same compound.

Lewis Hamilton, meanwhile, completed a full 66-lap Spanish Grand Prix simulation run to underline Mercedes' confidence in its F1 W07 Hybrid.

Bottas, second quickest for the day with a time 0.2s adrift of Rosberg but achieved using the new ultra-soft rubber, said: "At the moment it looks like they [Mercedes] are in a really strong position.

"Where we are now it looks like it's going to be quite tricky for anyone to challenge them at the beginning of the season. That is a fact at the moment.

"But let's see. I'm sure we'll still progress a lot from these tests and there is more to come."

Suggested to Bottas another season of Mercedes dominance would be a shame for the fans, he replied: "Yeah, I know. We are doing our best. We're really trying to chase them.

"It's a long season, and who knows. We'll hopefully have plenty of upgrades to come for Melbourne, and hopefully they will work well.

"Don't lose your faith yet."

For now, it would appear Williams will be challenging Ferrari to be the best of the rest.

Bottas said: "It was a good sign today we're starting to change the programme and do more and more performance work.

"The laptimes were coming down nicely, and we know we still have plenty more to come.

"We're trying hard to be up there, but whether we're going to there in Melbourne, we don't know yet.

"But we've definitely made progress, as have most of the teams. It's so difficult at this time to say anything in fine detail as to where we are.

"I do hope we can fight with Ferrari and Red Bull. It's going to be a competitive season. I just really hope we can be up there fighting for the places we want."