Here is why drivers find Singapore Grand Prix TOUGHEST...

‘It's a race I have enjoyed but it's always very long’

‘If it plays in your favour then you take it and if it works against you, it's quite annoying but that's the nature of a street circuit’

‘It's just heat and stale air. In Malaysia there's a bit of circulation, even though it's hot you get a bit of a breeze but here, no’

Since its inaugural race in 2008 the Singapore Grand Prix has gained a reputation for being the toughest challenge in Formula One, providing drivers with an extreme test of endurance in the trickiest conditions.

Raced under floodlights on a tight, 23-turn 5.065-km street circuit in downtown Singapore, the 61-lap trawl in tropical heat just north of the equator has been won by three men -- Fernando Alonso, Sebastian Vettel and Lewis Hamilton.

The exclusive triumvirate is made up of world champions, suggesting only the very best can master the Marina Bay circuit, but four-times winner Vettel believes luck can play as large a part as skill.

"It's a race I have enjoyed but it's always very long," said the German who triumphed last year.

"You can be lucky or unlucky with the safety cars, which is not what you hope for as a driver, you prefer it to be fair and square," added Vettel who also won the race from 2011-13.

"If it plays in your favour then you take it and if it works against you, it's quite annoying but that's the nature of a street circuit," he told reporters on Thursday.

Red Bull's Daniel Ricciardo, who was second behind Vettel a year ago and is hoping to go one better on Sunday, said there was no escape from the stifling heat in the cockpit and drivers got little respite for the duration of the race.

"It's similar in heat and humidity to Malaysia but you're surrounded by just the city and a lot of concrete so it's the one race I feel where you open your visor to get some air and you're not getting any reward for that," the Australian said.

"It's just heat and stale air. In Malaysia there's a bit of circulation, even though it's hot you get a bit of a breeze but here, no. It's a track that you can't.

"If you come here unprepared then you can't luck into a good result. You've got to come ready to go."

Finn Valtteri Bottas said drivers needed maximum concentration to ensure they survived unscathed.

"Physically at least it is the toughest race. Mentally, I think it feels a bit like Monaco. It's very intense and needs to be zero mistakes," the Williams driver explained.