Samsung Electronics Co. Ltd increased its lead over Apple Inc. and Nokia in the global cellphone market in the second quarter, helped by strong demand and large marketing campaigns for its latest flagship model, the Galaxy S III, according to a Reuters poll.

Samsung and Apple have been neck-and-neck for several quarters in the battle to be the largest smartphone vendor, but the May launch of the new Samsung model created a clear gap between the two, the poll of 41 analysts showed.

Samsung is expected to have sold 50 million smartphones in the quarter, compared with Apple's forecast sales of 30.5 million iPhones.

"Samsung is expected to be the smartphone hero in the second quarter," said IDC analyst Francisco Jeronimo. "We are also expecting to see the biggest smartphone volumes ever shipped from one single vendor in one quarter, driven by strong demand of the Galaxy portfolio, particularly the Galaxy S II and S III," he said.

Samsung is benefiting from its wide smartphone portfolio when competing against Apple, whose sales are dependent on launch schedules for the next versions of the iPhone.

In the overall cellphone market, when also including basic cellphones, Samsung ended Nokia's 14-year reign as the world's largest in the first quarter and is expected to stretch that lead. Samsung is estimated to have sold 15.7 million more phones than Nokia in the second quarter, the poll showed. In the first quarter, it sold 3.4 million more phones than Nokia, according to Gartner.

The poll also underscored the growing importance of Chinese vendors ZTE and Huawei in the industry.