US fastfood giant McDonald's has reported a 56% increase in quarterly net income, boosted by strong comparable sales and improved margins.

The company posted net income of US$511.5m, or 40 cents per share, for the first quarter to 31 March, compared to net income of $327.4m, or 26 cents per share, for the year-ago period.

First-quarter revenues increased 16% to $4.40bn, a rise of 8% in constant currencies. Systemwide sales increased 17% (10% in constant currencies), and comparable sales increased 9.4%. Operating income increased 27% to $858.4m.

Last week the company was hit by the sudden death of its chairman and chief executive officer Jim Cantalupo.

"My management team and I remain firmly committed to strengthening McDonald's relevancy and continuing the momentum that began under Jim's leadership," said newly appointed CEO Charlie Bell.

"We delivered impressive first quarter results fuelled by the overall performance of our US business, improved comparable sales across all geographic segments, and increased margins. We served 2.3 million more customers during the first quarter compared with the same period in the prior year - the equivalent of adding roughly 1,500 restaurants, yet we added only 100 restaurants over the past 12 months," Bell said.

The company said that to date in April, its US sales remain strong, and European sales trends have improved compared with March, following the successful launch of the Salads Plus menu in several key markets.