Uber has expanded its latest funding round amid investors' rising appetite for the ride-sharing app.

In a filing with the Delaware Secretary of State, the company said it is raising the size of its Series E funding round by $1bn (£650m, €878m) to $2.8bn, according to media reports.

In December, the company raised $1.2bn that valued the start-up at a whopping $40bn. It recently received an additional $600m funding from Chinese search engine Baidu and closed a $1.6bn convertible debt from Goldman Sachs's wealth management clients.

"The participation we have seen in Uber's Series E underscores the confidence investors have in Uber's growth," Nairi Hourdajian, Uber's head of global communication said in a statement.

Uber recently told some investors that it forecasts net revenue of more than $2bn in 2015, The Wall Street Journal reported, citing a person who was briefed on the matter.

That represents a five-fold revenue growth from 2014, when the company reported net revenue of more than $400m.

Uber is currently the second-biggest tech start-up in terms of valuation, behind Chinese smartphone manufacturer Xiaomi that is valued at $45bn.

Investors' rising appetite for the company comes despite the legal problems it faces in a number of countries and stiff competition from similar start-ups.

The US ride-hailing company, which has operations in more than 250 cities across the globe, is facing legal hurdles in South Korea, India and a number of European countries.

Earlier, Chinese taxi hailing apps, Didi Dache and Kuaidi Dache, said they have agreed to merge to form one of the world's largest companies in the ride-sharing sector.

The merger comes as another blow to Uber's global expansion plans.