Triple Formula One world champion Lewis Hamilton has accused some rivals of 'moaning' about safety at the Baku street circuit that hosts Azerbaijan's inaugural grand prix on Sunday.

"These drivers, they moan so much about so many things," the Mercedes driver told reporters after going fastest in Friday's free practice on a track that mixes very high speed straights with tight corners.

"It is really bumpy down the straight and you can't really see turn one that well and it's really hard, but that's a part of racing," added the Briton.

"These guys they want it to be smooth . . . smoother than ever, no vibrations and no bumps. They want to take all the character out of these tracks."

German team mate Nico Rosberg, the championship leader, and Jenson Button, Hamilton's compatriot and former partner at McLaren, both expressed concern on Thursday about the lack of run-off areas and the fast pit-lane approach.

Button, the 2009 champion, said it seemed the sport had gone backward on safety.

"The track is pretty cool. There are just some safety concerns at a few places like the pit entry, which we have to look into," Rosberg said on Friday.

The pit-lane entry comes off the 2-km straight, now the longest in the sport, and enters a chicane some time before the speed limiter has to be applied.

Drivers argue that, given the importance of fractions of a second, drivers will only slow at the very last moment which could cause a big accident.

The governing FIA said on Friday it was making some modifications to the track after bolts holding down kerbs at turn six came loose during first practice.