The car completed its first laps at Silverstone on Wednesday with Valtteri Bottas behind the wheel
Mercedes are "taking nothing for granted" this season, says team principal Toto Wolff.
The team, led by five-time world champion Lewis Hamilton, have won the past five constructors' championships.
Speaking at the launch of Mercedes' 2019 car, the AMG F1 W10 EQ Power+, Wolff said: "Every team can have a shot at the title and we're seeing all of them as a potential threat.
"There's absolutely no feeling of entitlement to be at the front."
He added: "The regulations have changed quite substantially.
"We have to start from scratch. We need to prove ourselves again - against our own expectations and against our competitors."
The season begins in Melbourne on 17 March. Briton Hamilton, who won his fifth world title last year, will lead Mercedes again alongside Valtteri Bottas for the third season.
"2018 was a great year, but I feel like 2019 can be even better," Hamilton said. "I want to achieve more. I want to continue to keep pushing."
What has changed with the new car?
Work on the revamped Mercedes started 16 months ago, before the end of the 2017 season.
There is an improved power unit and the car has been designed around new regulations aimed at making the racing closer by reducing the disruption caused to the aerodynamics of a car following another.
The car has a similar silver livery and branding to last year but has changed substantially under the skin
"Regulation changes are both opportunity and threat," said technical director James Allison.
"They are an opportunity because all the old assumptions about what you need to have to be quick are swept away and, if you are fleet of foot and smart in dealing with that, you can do better than all the other teams that are tackling the same change.
"They are a threat because if you are not as smart and you didn't see how to make the most of these new regulations, then you'll certainly suffer in the coming season.
"We have worked hard on the suspension and aerodynamic characteristics to deliver a car that will be much kinder to its tyres."
Lewis Hamilton has been the dominant figure in the sport for the last number of yearsWhat has Hamilton been up to?
Hamilton, 34, has kept a relatively low profile over the off-season, spending time in the United States, where he attended the Super Bowl this month.
"I had a great Christmas with my family and then I went snowmobiling, I went skiing, I went surfing with Kelly Slater, which was amazing," he said.
"I completely switched off from racing for a while, trying to focus and re-centre myself and training hard for the new season."
Wolff added: "When we met after the winter break, Lewis was refreshed. He's extremely hungry and wants to start racing again."
