* Leclerc fastest in afternoon, Hamilton in morning
* Bottas and Verstappen both crash
* Kerb damage a talking point (Adds second session, quotes)
SPIELBERG, Austria, June 28 (Reuters) - Valtteri Bottas and Max Verstappen crashed in an accident-strewn Austrian Grand Prix practice on Friday while Charles Leclerc stayed out of trouble and sent Ferrari back to the top of the timesheets.
Bottas was sent to the medical centre as a precaution after smashing head-on into the barriers at the downhill turn six, with his badly damaged Mercedes brought back to the pits on a truck.
The incident on a gusty day at the Red Bull Ring brought out red flags for the second time in an error-strewn afternoon session, with last year's race winner Verstappen also caught out.
His Red Bull slammed backwards into the tyre wall at turn 10, breaking the rear suspension.
"I made a correction and it was a bit too late," said Bottas, who is second in the championship and a hefty 36 points behind team mate Lewis Hamilton after eight rounds all won by Mercedes.
"This afternoon is a bit more windy and obviously the track is very penalising on making mistakes."
Leclerc's best effort was a lap of one minute 05.086 seconds, leaving Bottas second.
Verstappen, who ended up ninth in the second session, had complained earlier about losing the rear of the car in shifting winds.
"This year the cars in general are more sensitive to the wind, as you could also see I think with Valtteri," said the 21-year-old Dutch driver.
Five-times champion Hamilton set the pace in the morning, with Ferrari's Sebastian Vettel splitting the two Mercedes, in 1:04.838.
The Briton was only fourth after lunch with Red Bull's Pierre Gasly third.
Vettel almost became another casualty after spinning off but the four-times champion stopped short of the tyre wall and kept the engine running.
Bottas, on pole for the past two years in Austria, was third fastest in that opening session but his morning had already started with a flurry of activity in the garage.
Mercedes carried out a hurried engine change after discovering an oil leak on his car about an hour before the start of the session.
"It was a bit messy, overall," Mercedes team boss Toto Wolff said of his team's morning, with the track's aggressive kerbs a focus of debate after several teams suffered costly front wing damage.
The first session ended three minutes early after Renault's Nico Hulkenberg ran over the kerb at the penultimate corner and ripped off half of his car's front wing, scattering debris across the track.
That was just one of several incidents involving the kerbs.
Red Bull boss Christian Horner said they had already cost his team some 250,000 pounds ($318,125) in damage and suggested the angle needed changing.
"There's been a lot of discussion about these kerbs here over the last couple of years. I'm sure there's going to be a lot more," he added.
Hamilton has won the last four races, and six out of eight this season, with Mercedes favourites to take an 11th victory in a row at a circuit where last year they suffered a double retirement.
That would equal the longest winning streak of the modern era set by McLaren in 1988.
Teams earlier voted on whether to return to last year's thicker treaded tyres for the rest of the season, a move seen by some as an attempt to reduce Mercedes' advantage. There was no majority so nothing changed.
"Relying on the teams to agree, that was never going to happen," said Horner.
($1 = 0.7859 pounds) (Reporting by Alan Baldwin in London, editing by Christian Radnedge)