More than a million National Grid gas customers in Brooklyn, Queens and Staten Island face three years of wallet-busting rate hikes starting Sunday.

A National Grid home-heating customer in New York City who uses 1,000 therms of gas per year faces rate increases of 9.4 percent this year, 9.2 percent in 2018, and 10 percent in 2019, company data show.

Customers in the Rockaways and on Long Island face smaller hikes.

State regulators admit the hike will be significant.

“Rate shock is an obvious concern,” the state Public Service Commission said.

“They are entirely correct to worry about customers opening up their bills and their eyebrows hitting the ceiling,” said Richard Berkley of the Public Utility Law Project, a consumer watchdog.

It has been a decade since the state last raised National Grid’s rates for delivering natural gas.

National Grid says its infrastructure costs are growing, and that the hike in its charges for delivering gas will buy upgrades to gas lines and other equipment.

National Grid called the state approval “fair and reasonable.” The company says it will spend $3 billion of the rate hike improving the infrastructure that serves its 1.2 million city customers.

National Grid also will need tens of millions of dollars to clean up its polluted properties along Newtown Creek in Brooklyn and Queens and the Gowanus Canal in Brooklyn.

National Grid’s total charge to typical New York City residents will be about 31 percent higher in 2019 than in 2016. But observers say that when the cost of gas itself is subtracted from the rates, the utility’s take from its New York City customers will rise by about 50 percent.