Britain’s triple world champion Hamilton had started on pole position, with Rosberg alongside on the front row at the Circuit de Catalunya.
The German, aiming to make it five successive wins for the season, passed Hamilton around the outside of turn one and the Briton was then squeezed on to the grass as he tried to regain the lead at turn three.
His car skewed sideways and smashed into Rosberg’s, with both drivers ending up in the gravel and the safety car deployed.
Watching Daimler chief executive Dieter Zetsche shook his head in dismay, while Hamilton threw his steering wheel out of the car.
The pair returned to the paddock on scooters and trudged up the stairs for a debrief with Mercedes team bosses, motorsport head Toto Wolff hot on their heels, before also seeing the stewards.
The team’s non-executive chairman Niki Lauda, a triple world champion himself, blamed Hamilton before going to see the drivers.
“It is stupid, we could’ve won this race,” the Austrian told the BBC. “Lewis is too aggressive. I need to talk to them and hear their explanation and then we will see what happens.”
Rosberg still has a comfortable lead in the championship standings, being 43 points clear of closest rival Hamilton before Sunday’s race.
However, the collision ended Mercedes hopes of extending the team’s winning run to 11 races and equalling McLaren’s 1988 record streak of success.
Only one driver in the modern era has won eight consecutive races – Germany’s Sebastian Vettel, with nine in a row in 2013 for Red Bull - but Rosberg had hopes of continuing his run after winning at the circuit last year.
Victory would also have made him only the third F1 driver after compatriot Michael Schumacher and Britain’s Nigel Mansell to win the first five races of a season.
Original source: Nico, Lewis take each other out