Nico Rosberg beats Lewis Hamilton before tyre explosion

Nico Rosberg beat team-mate Lewis Hamilton to set the pace in an eventful second practice session at the Belgian Grand Prix.

The German then hit trouble when he suffered a spectacular right-rear tyre failure while close to 200mph.

"Definitely not fun," Rosberg said. "It was at maximum speed, so not good."

Rosberg was also quicker in the first session, heading Hamilton by 0.302secs as the world champion appeared to struggle to get a feel for the track.

The incident caused him to spin and the session was stopped to clear the track.

Pirelli said it was investigating the cause of the failure, which happened in the section heading towards the Blanchimont corner, one of the most demanding curves on the track, which is among the toughest on the calendar.

"It was not a nice experience," said Rosberg. "A 360 degree spin at 200mph 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."

Rosberg said he did not think he had run over debris to cause the puncture.

Television pictures showed that a narrow band of the tyre cord had started to come free of the structure earlier in the lap and become progressively worse as he went through the middle sector, which is packed with demanding corners.

No sooner had the cars rejoined the track after a stoppage, Marcus Ericsson crashed at the 150mph double left at Pouhon, causing another red flag.

In terms of competitiveness, Red Bull, whose car has made significant steps forward in recent races, appeared to be ahead of Ferrari as best of the rest behind the Mercedes of Rosberg and Hamilton.

Daniel Ricciardo and Daniil Kvyat took third and fourth ahead of Ferrari's Kimi Raikkonen, with Sebastian Vettel 10th.

Raikkonen's time was matched to the thousandth of a second by Force India's Nico Hulkenberg, with Lotus's Romain Grosjean 0.028secs further adrift in seventh.

The Saubers, running for the first time an upgraded engine Ferrari have had since Canada in June, were eighth and ninth with Marcus Ericsson and Felipe Nasr.

After a crash in the morning delayed his start to the session, Lotus driver Pastor Maldonado had a near-miss in the afternoon.

The Venezuelan ran wide on the exit of the Paul Frere corner and then rejoined right in front of the Williams of Valtteri Bottas as they approached the flat-out Blanchimont corner.

There was no sign of the promised major step forward from the McLaren-Honda thanks to the upgraded engine they have brought to this race.

Jenson Button and Fernando Alonso were 17th and 18th fastest, with the Englishman 0.7secs ahead of the Spaniard after Alonso failed to record a time on the faster tyre as a result of a mistake at the Bus Stop chicane on his lap.

Full practice results

Belgian GP coverage details