Nico Rosberg topped the times ahead of his Mercedes team-mate and defending two-time world champion Lewis Hamilton in Friday morning's opening free practice session for this weekend's Belgian Grand Prix.

Rosberg, whose wife Vivian is expected to give birth to their first child at any time, clocked a best lap of one minute and 51.082 seconds to take command in the first action following Formula One's four-week mid-season break.

Championship leader Hamilton was second-quickest, adrift by slightly more than two-tenths of a second, as the pair demonstrated their continuing supremacy and the rivalry that exploded into acrimony and a collision during last year's Belgian race.

On a bright and sunny morning in the Ardennes, where overnight rumours of a threatened blockade of the circuit by dairy farmers preceded the action, Hamilton had set the best lap time after 20 minutes following an impressive early display by local hero Dutch teenager Max Verstappen of Toro Rosso.

The 30-year-old Briton stayed on top until the final 30 minutes when Rosberg responded and then trimmed his times, having recovered from earlier problems when his car had lost drive and required a pit stop for repairs.

Australian Daniel Ricciardo was third fastest in his Red Bull ahead of Finn Kimi Raikkonen, fresh from re-signing with Ferrari for next year, and his team-mate four-time champion German Sebastian Vettel. It was a strong early show from Ferrari to mark their 900th race in Formula One.

The session was interrupted by a crash when Venezuelan Pastor Maldonado lost control and wrecked the front right section of his Lotus car. The action was red-flagged, but Maldonado was unhurt and after a short pause to clear debris, the session resumed.

Russian Daniil Kvyat was sixth in the second Red Bull, continuing the form that saw him shine in last month's Hungarian Grand Prix, ahead of Verstappen and his Toro Rosso team-mate Spaniard Carlos Sainz.