Japanese auto giant Nissan said Monday its nine-month net profit jumped 18.4 percent as it benefited from a weaker yen and accelerating sales in North America and its key China market.

The buoyant figures come after rival Toyota, the world's biggest automaker, last week tipped a record annual profit with nine-month earnings more than doubling to $15 billion.

Nissan, Toyota and Japan's number-three automaker Honda have been big winners over the past year as a sharp drop in the yen inflated exporters' repatriated profits, further boosted by improved demand in key overseas markets.

Sales in China slumped in late 2012 and into last year as a Tokyo-Beijing diplomatic row sparked a consumer boycott of Japanese brands in the world's biggest vehicle market. Relations remain tense, but Japanese manufacturers have reported sales are returning to pre-spat levels.

Nissan was particularly vulnerable as it counts on China for about a quarter of its sales and has been fighting off rivals, including General Motors and Volkswagen, to scratch back to its pre-boycott 7.7 percent market share.

In November, the new executive in charge of Nissan's China business said it had gone from suffering in China to struggling to catch up with rebounding sales in the world's biggest vehicle market.

Nissan, maker of the Altima sedan and luxury Infiniti brand, has three plants in China with a local partner and plans for another factory to open this year.

On Monday, the firm said it earned 274.1 billion ($2.68 billion) in the April-December period on sales of 7.27 trillion yen, a rise of 19.7 percent from a year earlier.

For the nine-months, Nissan sold 3.67 million vehicles globally, up 1.0 percent.

"Nissan has delivered a solid nine-month performance amid growing demand for new models in several key markets," the company's chief executive Carlos Ghosn said in a statement.

"Sales in Japan and North America helped offset emerging market volatility and sluggish conditions in Europe. Based on its strong product line-up and current market demand, Nissan is maintaining its full-year earnings guidance."

In November, Nissan downgraded its fiscal full-year profit outlook to 355 billion yen from an earlier estimate of 420 billion yen.

Despite the buoyant figures so far, an April sales tax hike in Japan and possible slowdown in US and Asian markets could put the brakes on sales for the Japanese auto sector, said Takaki Nakanishi, analyst and chief executive at Nakanishi Research Institute in Tokyo.

"The Japanese auto industry has been on the upswing thanks to the weak yen and strong demand in the US and Asia, including in Japan," he said.

"But there are some negatives on the horizon. The sales tax hike in Japan will affect auto sales for sure, although I think the impact is likely to be limited. Also, the recent strong demand in Asia and America is likely to lose its momentum."

Gains from the weak yen will taper off, he added, while political unrest in Thailand, a major production base for Japanese automakers, could also dig into results.

Still, the upbeat results marked a firm recovery for Japanese automakers after the 2011 quake-tsunami disaster hammered production and disrupted their supply chains.

Honda has said its nine-month net profit surged almost 40 percent to 403.60 billion yen.

In Tokyo, Nissan shares closed 0.11 percent higher at 885 yen before the earnings report was released.