NEW YORK — European telecommunications and cable company Altice has agreed to buy New York cable operator Cablevision for $17.7 billion, including debt, according to a person familiar with the matter.

The person spoke on condition of anonymity because the deal had not been formally announced. The announcement is expected before European financial markets open Thursday.

The move is part of Netherlands-based Altice’s aggressive expansion in the U.S. It announced a $9.1 billion deal for Suddenlink, a smaller cable company based in St. Louis, in May.

Shares of Cablevision Systems Corp. jumped 16 percent to $33.12 in after-hours trading Wednesday.

U.S. cable companies have been in a merger frenzy over the past few years as people increasingly drop their TV packages and watch video online from competitors like Netflix, while cable companies’ costs for sports and other channels rise.