Lewis Hamilton should keep his composure to secure victory in this year's world championship, according to Nico Rosberg, who beat his former Mercedes teammate to last year's crown before suddenly retiring.

The pair had a difficult relationship at the German team, but Rosberg says that he has been impressed with Hamilton's season this year.

"He's on an incredible run at the moment," Rosberg told Austrian newspaper Kronen Zeitung.

"At the same time everything has been going wrong for Sebastian Vettel," he added, amid reports that Hamilton could wrap up the title this weekend in Austin.

Rosberg thinks the key to Hamilton's run of form is confidence and consistency.

"Lewis is showing an unbelievable consistency," he said. "And that is so difficult to do from race to race."

However, Rosberg warned that Hamilton cannot now sit back and cruise to the championship, despite his 59-point lead with just four races to go.

Asked to compare Hamilton with Ferrari's Vettel, he said: "I'd say Lewis is a little better in pure speed on a lap.

"But his weakness is his emotional ups and downs, which is where I see Sebastian with a small advantage. At such a high level, even little things play a big role.

"If something is bothering you or you're putting energy into something else, it can throw you off. It happened to Lewis last year, when the Snapchat thing happened in the press conference and then he had the fight with the angry media.

"It's wasted energy, especially in the decisive phase of the world championship. Anything like that can throw off your concentration."

Nonetheless, Rosberg said that he thinks Hamilton will win the 2017 title, even if it means the exciting duel to the finale with Vettel will not take place.

"I am neutral now," he said, "but as a fan, what happened in Japan was very bad. Everyone wanted to see a fight until the end.

"I'm sure even Lewis would have loved to fight until the last minute, but that's motor sport. In any case, Mercedes and Lewis still cannot sit back even now."

Hamilton would clinch his fourth drivers' title with victory this year.