Sebastian Vettel is third in the drivers' championship with 52 points

Ferrari's Sebastian Vettel says Mercedes consistent success in Formula 1 is "boring".

The world champions have taken one-two finishes in the first four races of 2019 - after winning the past five drivers' and constructors' titles.

"Boring, isn't it?" Vettel said. "So boring. It's not just four races. It has been four years, more or less."

But the German, 31, believes Ferrari have the potential to challenge Mercedes this year.

"[We have to] work harder, work better. We are pushing as hard as we can," Vettel, who won four consecutive titles with Red Bull from 2010 to 2013, said.

"But you need to respect that they are doing phenomenally well and getting their cars most of the time in the right place.

"But I'm confident. I believe in this team and I know we can improve. I think we have a good car. We just haven't managed yet to put it always where it belongs, so it is difficult to have the trust and the feel, but I am sure it is going to turn around."

Ferrari are second in the constructors' championship on 99 points, behind Mercedes who have 173 points

Vettel said Ferrari knew they had a quick car but were struggling to get the best out of it.

"It's like a Rubik's Cube," he said. "We just need to solve it. We have a lot of people who can do the Rubik's Cube in a couple of minutes. We have really clever people but we are working on a large-size Rubik's Cube."

Team boss Mattia Binotto added: "Obviously four races into the season, no win for Ferrari, four wins for Mercedes, no doubt they are very strong.

"Certainly they have got a slightly better car, but I think that the gap is not so big and the points are not reflecting the true potential of the cars."

Binotto pointed to the pace shown by Ferrari's other driver Charles Leclerc - who dominated in Azerbaijan at the weekend until crashing in second qualifying on Saturday - as evidence of the team's potential.

"With Charles, we [had] the potential for pole, and if you've got a car fast enough to score potentially the pole, you've got a good car overall," he said.

"In the race, yes, we weren't as fast as them, but we didn't finish 20 seconds behind."

Leclerc also lost out on a potential win after dominating in Bahrain at the second race of the season, when he suffered an engine problem that dropped him from the lead to third in the closing laps.

The 21-year-old, who finished fifth in Baku on Sunday after starting eighth on the grid, said: "The performance was there to do pole position but it was my mistake.

"I need to work on these things. I am only on my second season in F1. It is not [a case of looking] to find excuses, I should not do these mistakes but I take it as part of my path and learn from it.

"At the moment we have not had four perfect weekends. I think on performance we are not so far [away], in qualifying especially. In the race, they seem to have more for now but we will work and come back stronger."

Valtteri Bottas' win in Azerbaijan was his second of the season

Mercedes driver Valtteri Bottas leads the championship by one point from team-mate Lewis Hamilton, with Vettel 35 points behind. Red Bull's Max Verstappen is one point behind Vettel, and Leclerc a further four adrift.

Hamilton dismissed suggestions that Bottas was already the only rival standing in the way of his sixth world title.

"No it is far too early to say one person is the title rival," Hamilton said. "Ferrari have had the pace in practice in qualifying. If both drivers had delivered as we did, it would have been a lot closer.

"We have to stay on our toes. We didn't bring an upgrade and Ferrari did, so it's a little bit of a surprise.

"We will go [to the next race in Spain] and Ferrari looked quick there in testing and I am sure they will bring extra upgrades.

"These first four [races] have been stellar for us and we just have to stay on our toes because you just never know when another team is going to take a step forward. We have to continue to perform as we have and not let that waver."