"They've a very strong team, a good group of people, good drivers so it looks to me at the moment they're the main challenge to us," said team owner Ross Brawn [ Images ] after Sunday's Spanish Grand Prix [ Images ] handed him a one-two with Button taking his fourth win in five races.
"Other teams will come and go during the season, but in terms of a long-term challenge then Red Bull look very strong."
Red Bull's Australian Mark Webber [ Images ] was third and Vettel fourth in Spain.
The German had started on the front row alongside Button and would have challenged for the victory had he not been overtaken by Ferrari's [ Images ] Felipe Massa [ Images ] at the start and then spent most of the race behind the Brazilian.
"If Vettel had a clear track, he would have given us a very hard time," said Brawn. "He had a lot in hand but just couldn't use it, which is the second race he has not been able to show what he can do."
Brawn said his Mercedes-powered team's astonishing start to the season, turning the sport upside down after emerging from the remains of now-departed Honda, was partly due to their new status as an independent and the struggle for survival.
"We don't have a manufacturer stood above us, we are doing it for ourselves, so there's a little bit of freedom in that and maybe that is why the team is shining at the moment," said the former Ferrari technical director whose old rival and former McLaren [ Images ] designer Adrian Newey is now at Red Bull.
"We are fighting tooth and nail to win every race and do as good a job as we can.
"The team is performing well, the drivers are performing well, the factory is working well, the engineers in the briefings are solid, people are working diligently at making the car better and the pit stops are perfect," he added.
"So it's a team that has really come together. The adversity of the winter seems to have gelled everything even more. Everything is running like clockwork at the moment.
"We all know destiny is just around the corner, so we are being cautious."