Argentina legend Maradona says Germany's powerful performance in their 4-0 win over Portugal is cause for concern amongst the other World Cup favourites.

"We saw a devastating Germany, a Germany who roamed around with perfection," the 1986 World Cup-winner told his Venezuelan television show "De Zurda".

"They caused a bit of worry with their physical strength."

Thomas Mueller became the first player to claim a hat-trick at Brazil 2014 as Cristiano Ronaldo's Portugal were outclassed after centre-back Pepe's first-half dismissal in Salvador.

Former Argentina coach Maradona got a taste of Germany's power four years ago in South Africa when his team was hammered 4-0 in the quarter-finals.

Maradona said he was impressed by the Germans' "very, very intelligent lines of running" against the Portuguese in their Group G opener.

"If Germany keep this rhythm, then they must be taken seriously," Maradona added.

The Argentina legend has already nicknamed Germany's hat-trick star Mueller 'El Flaco' -- the Skinny One.

"He has no muscles, but today he tore them apart," added an impressed Maradona.