World champion Lewis Hamilton expects a tougher challenge from Ferrari in Formula 1 this season.
Ferrari had the car to win the 2018 title but fell away after a series of errors, with Hamilton taking a fifth championship for Mercedes.
But Ferrari impressed with strong pace at the start of pre-season testing.
Hamilton said: "Ferrari are very strong. It appears they have a better package than last year, which means it will be a bigger challenge for us."
But the 34-year-old cautioned that it was premature to jump to too many conclusions after just two and a half days of pre-season testing.
He said: "They have been looking great. We have just been digging deep, trying to understand the car, pretty much the same as the beginning of every year.
"Ferrari always look strong, particularly the last few years; they looked strong right at the beginning, so that's to be expected. It has been normal."
Hamilton is going for a sixth world title this season, having won four of the last five championships, and his Mercedes team are going for a record sixth driver and constructor titles in a row.
But Hamilton said he had detected no complacency at the team, just a focus to keep winning despite the technical rule changes for this season aimed at improving the racing.
He said: "I am competing with everyone. I don't know who's going to be quickest. You can't say just Ferrari. You don't know where the Red Bulls are. Who knows what people are going to bring up for the first race?
"At the moment, we are competing against our past selves. All the engineers are raising the bar.
"It has been super impressive to see the hunger is still there after all the successes we've had.
"It has been a difficult winter for the guys back at the factory, I can see it and I've heard from them, with the rule changes, but if anyone can do it, it's my guys.
"We are the only team to have won a championship in a cross-over rule situation (in 2017) and even if we don't start on the right foot, I feel confident (we can do it again)."
Hamilton said he had taken advantage of new rules governing the weight of cars - aimed at ending penalties for taller, heavier drivers that were inherent in the previous system - to change his training and add more muscle bulk.
"I feel in the best shape I have been in for round seven with the team," he said.
"Crazy to think I have been six years with the team but this is going to be the most challenging year of our partnership (...) so it is super exciting. I still love racing so nothing really changes there."
He said he was not allowing himself to think about winning the championship: "It is a new season, a new year, a new chapter and we have to approach it like it's our first. We're going for number one, that's how I approach it."
And he added he was as motivated as ever to win.
"I have earned the right to be here and (I'm) still delivering, at least last year, better than ever," he said.
"And I love that challenge of coming back each year, new car, it is like meeting someone new, and you don't know the good and bad, and the journey you go on with that car is a real privileged position.
"I love getting back in and giving it another shot and you put the title out there for anyone else to take.
"I love that fight, and even more so the work you do with almost 2,000 people.
"The driving is cool but going back and seeing how far your word travels and working on new technology and being only one of two that gets to pilot it, it's the best job in the world. What else would I do afterwards? I could do many things but this is at the core of me and this is what I love doing."