Jenson Button believes "people will be surprised" by how competitive Marussia is at the Australian Grand Prix.

Max Chilton ended the second Bahrain test with a best time around three and a half seconds slower than the ultimate pace set by Felipe Massa. However, Button spent a section of his running on Friday following Jules Bianchi in the Marussia and he said the car looked much stronger than in previous years.

"It's interesting to see suddenly as teams update their cars there are a lot more teams that are competitive, gaining seconds here and there over the last couple of weeks," Button said. "There are a lot of teams that are strong at the moment. Even following the Marussia they look so much better than last year's car, through high speed ... I think people will be surprised how competitive they are actually."

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While Marussia is running a Ferrari engine for the first time, Button still believes the Mercedes will prove the most reliable come Melbourne. Asked if he felt his car was bulletproof, Button replied: "None of them are.

"In a way I'm very happy how reliable the cars have been, I'm surprised in a way. Mercedes have done a great job in the power unit, I really do, and it looks like Renault and Ferrari have gained a lot of pace and reliability. But I'm very happy to be with Mercedes right now for reliability reasons."