Stock markets plunged around the globe Thursday and Friday, amid new concerns that the world may be headed for another sharp economic downturn.

In Asia, markets fell Friday, with Tokyo's Nikkei closing down 3.72 percent and hitting its lowest level in five months. Hong Kong's Hang Seng tumbled more than 4.5 percent in afternoon trading.

European markets are expected to open lower Friday after falling nearly 4 percent Thursday.

In the United States, the Dow Jones Industrial Average plummeted 513 points, or 4.3 percent Thursday, its largest drop since October 2008. Other major stock indexes, the NASDAQ and the S&P 500, also fell sharply.

Financial analysts say investors are concerned the U.S. economy could be headed back into a recession.

A U.S. report showed new evidence of the country's weak labor market.

A total of 400,000 unemployed workers made their first claims for jobless benefits last week, a figure that was down slightly from the week before. Financial experts say the figure has to drop to below 375,000 and stay there awhile to give U.S. companies enough confidence in the national economy to hire more workers.

On Friday, the U.S. is releasing its monthly unemployment report for July, but experts do not think it will be changed from June's 9.2 percent figure.

The U.S. has the world's largest economy, but investors have voiced little confidence in the country's sluggish recovery. They shrugged off the impact of the agreement this week by U.S. President Barack Obama and Congress to increase the nation's borrowing limit and avoid an unprecedented default on the government's financial obligations.