Mercedes team boss Toto Wolff has admitted that he is impressed by how much Ferrari have improved since last season, and predicts that Sunday's Bahrain Grand Prix will closely fought.

Mercedes dominated last season, winning 16 of 19 races, but this year Ferrari are much closer and claimed victory in the Malaysian Grand Prix through Sebastian Vettel.

Lewis Hamilton will start on pole tomorrow, ahead of Vettel.

Wolff told reporters: "What you saw first was race pace and clearly what you have seen today is qualifying pace. Their rate of development is very impressive. It has been very impressive over the winter and has been impressive over the last three races so clearly that is quite a challenge for us.

"I expect the Ferraris to be strong and if the Ferraris are strong then we are going to see four cars pretty close to each other at the beginning. That could well mean that you need to have various strategies in place to react or to be proactive or reactive.

"It depends where each of the cars is and how the race pans out."

Nico Rosberg will start third on the grid for Mercedes, while Ferrari's Kimi Raikkonen lines up fourth.