More than 800 World Trade Center rescue and recovery workers have died since 9/11 — and cancer has killed at least 270 of those heroes, new data show.

The figures also show that 33 WTC responders committed suicide.

State researchers have tallied 817 deaths of workers and volunteers who toiled at toxic Ground Zero or the Fresh Kills landfill, where rubble was sifted.

“It’s still a huge undercount,” a source told The Post, adding that cases were still being collected.

The state Health Department’s WTC Responder Fatalities Investigation has so far reviewed death and medical records in 642 cases and found 479 responders who succumbed to illness, including cancers.

Another 149 suffered “traumatic deaths” in such incidents as drug overdoses, car crashes, fires and assaults — including 27 who died in the line of duty.

Another 12 died while serving in the military in Iraq and Afghanistan.

The number of deaths documented has soared since last September, when researchers listed 664 fatalities and confirmed 224, including 94 cancer cases. The rise is largely due to city agencies and WTC medical programs sharing more records, officials said.

About 50,000 firefighters, cops, EMTs, other workers and volunteers joined in the 9/11 rescue and recovery.

Cancers killing the most WTC workers include those of the stomach, colon, liver and other digestive organs (80), lung and throat (69), and blood cells, such as leukemia (37).

Another recent study found blood cancers hitting responders at ages much younger than normal.

Last month, cancer claimed veteran firefighter John McNamara, 44, of Engine Co. 234 in Crown Heights, Brooklyn. He had logged about 500 hours in the smoky WTC pit searching for victims and later helped in New Orleans after Hurricane Katrina. He left a wife, Jennifer, and a 2-year-old son, Jack.

“Guys with cancer are swept under the rug,” he had told The Post.

McNamara was diagnosed with advanced colon cancer in 2006 at age 41 — about 10 years before colonoscopy tests are recommended.

He urged more screening of firefighters to look for early warnings.

“How many of the thousands of guys who retired after 9/11 have polyps or tumors they don’t even know about?” he asked.

The 33 suicides did not surprise experts. Many responders cracked under the stress of health, financial and emotional problems, said Michael Arcari, an ex-NYPD official and director of Faithful Response, a mental health program for 9/11 responders.

“I believe the number is higher, based not just on what they went through at Ground Zero, but in the aftermath –how it turned their lives and families upside down,” Arcari said.