Nico Rosberg was fastest for Mercedes in Belgian Grand Prix practice today despite an explosive, high-speed tyre blowout that had the German wrestling to keep the car out of the barriers.

After lapping fastest in bright and sunny morning conditions, Rosberg went quicker in the afternoon before flirting with disaster.

"That was definitely not fun," he told reporters after escaping unscathed from the heartstopping incident in which the right rear tyre shredded in seconds as he approached Blanchimont at full throttle.

"It was not a nice experience. A 360-degree spin at 200 mph is not something you expect at all. Luckily I did not hit the wall. I didn't feel anything before, there was no warning. There will be a big analysis. I was feeling quick before then, comfortable."

Video evidence suggested the tyre had started to fray several corners before.

Rosberg, whose wife is due to give birth to their first child next week, kept the car on the track but the session was stopped for marshals to pick up debris scattered across the track.

The red flags came out again shortly after practice resumed when Sweden's Marcus Ericsson pitched his Sauber into the barriers.

"I hit the wall quite hard, sorry," he told his engineers over the radio.

The order at the top was the same in both sessions, with Rosberg ahead of team mate and championship leader Lewis Hamilton with Red Bull's Australian Daniel Ricciardo third fastest.

Hamilton, who reported no problems with his car, leads Rosberg by 21 points at the midpoint to the season with Belgium the first race after the August break.

The drivers had got back to work in predictable fashion in the opening session, with Venezuelan Pastor Maldonado crashing his Lotus, while champions Mercedes set the pace on the longest circuit on the calendar.

Rosberg's best morning time was one minute 51.082 seconds, despite an engine problem limiting his track time, with a 1:49.385 in the afternoon.

Maldonado, living up to the unfortunate 'Crashtor' moniker that has kept his mechanics busy, brought out the red flags after 50 minutes when he lost control at Malmedy and smashed into the barriers.

A website chronicling the Venezuelan's unhappy status (  promptly changed its status from 'Nope' to 'Yes!' and reset the clock for the next update.

Ferrari's Kimi Raikkonen, a four-times winner at Spa, responded to being given a new contract for 2016 by lapping fourth and fifth fastest in the respective sessions.

Four-times world champion team mate Sebastian Vettel was fifth and 10th.

Belgian-born Dutch teenager Max Verstappen, the closest to a home driver the local fans have to cheer on this weekend, was seventh fastest for Toro Rosso in the morning.

McLaren again struggled, despite upgrades to the Honda engine, with Fernando Alonso and Jenson Button languishing well down the field and hit by heavy grid penalties for engine changes.

Alonso was given a 30-place drop, while Button was demoted 25 places, ensuring both will start last on Sunday.