Lewis Hamilton expects Red Bull to be a major threat in China this weekend and says the battle for the Formula One drivers' title is wide open.

The defending champion took the chequered flag in Bahrain last time out having reversed the one-two with Mercedes team-mate Valtteri Bottas from the season-opening Australian Grand Prix.

Max Verstappen completed the podium in Melbourne, but Red Bull struggled to replicate that promise in Bahrain where Ferrari new boy Charles Leclerc was third after a mightily impressive showing.

Most pundits predicted that this season would once again see Hamilton and Ferrari's Sebastian Vettel vying for supremacy.

Hamilton, though, believes the early evidence suggests otherwise.

"At the moment it's clearly not just me and Sebastian," he said, in quotes reported by F1's official website. 

"So, I don't see that changing any time soon. At the moment it's at least four of us and the Red Bulls, you definitely can't count them out.

"They've had a bit of a slower start, but I think if you look at last year for example they won the race here and they particularly finished strong. I anticipate it could be something similar.

"On the straights they've been really good so they are clearly, whereas they usually have a really strong car and not so strong engine, it's the other way this year. 

"They've got not as strong a car. But they're one of the teams that can develop at a similar rate to Ferrari and us so it's far too early to say.

"The first few races of every season are really difficult to kind of judge.

"Obviously we didn't expect the performance we had at the first race, we didn't expect to see what we saw at the second race. It's only the third race."

Daniel Ricciardo steered Red Bull to victory in China 12 months ago, but heads into this season's race with new team Renault with a pair of DNF's to his name.

The amiable Australian believes perhaps he and the team are trying to be "too clever" in their approach.

"One thing we've assessed is maybe we're actually trying to do too much over the course of the weekends," he said. 

"We got the chance to analyse on the Monday after [Bahrain] and we established that we're maybe currently trying to do too much, where I'm trying to settle in and also my engineers are trying to [learn how to] work with me. And probably all of us, we're trying to be too clever as well.

"I don't want to say that, because you're always trying to find the limits. But for now, maybe we need to keep a more basic approach and just do what we can, do it well and then probably not look for that extra one per cent at the moment."