Vettel beat Mercedes’ previous benchmark by 0.286 seconds but said Mercedes remained favourites ahead of the first race in Australia on 24-26 March.
But Hamilton said: “I think Ferrari are bluffing and that they are a lot quicker than they are showing.
“They are very close, if not faster.”
He added: “It’s difficult right now to say who is quicker.”
Vettel’s time on Thursday of one minute 19.024 seconds beat the previous best of the seven days of testing, set by Hamilton’s Mercedes team-mate Valtteri Bottas. Friday is the final day of on-track preparation before the cars fly to Melbourne.
Vettel said: “If you look at the amount of laps Mercedes has done, at how slow they go in testing historically, how much they can ramp it up for races, it’s clear.
“They’re very fast if you look at their long-run pace. They’re the ones to beat.”
Vettel, who set his quickest lap on the “ultra-soft” tyre while apparently lifting off briefly before completing the lap to disguise his full pace, was also impressive in being just 0.3secs slower on the “soft”.
The “ultra-soft” is said to be about 1.2secs faster than the soft tyre.
Hamilton was second fastest, 0.328secs behind Vettel, also using the ultra-soft.
Source : Internet