When a forklift is used to carry a char-grilled hamburger patty to its bun you know this is one mega burger.

The giant burger weighing 777 pounds (352kg) has broken the record in the United States to make it into the Guinness World Records as the world's largest commercially available hamburger.

It was created on the world's biggest barbecue, Juicys Outlaw Grill, and included mustard, mayonnaise, pickles, onions, lettuce and tomatoes.

"They began at 5am with 600 pounds of meat, which they expected to shrink to about 400 pounds during cooking," The Oakland Tribune reported.

"They forged 340 pounds of dough into two buns. On standby were 50 pounds of cheese, 20 pounds of onions, 12 pounds of pickles, 30 pounds of lettuce and 10 pounds each of mustard and ketchup.

"The final burger weighed in at 777 pounds, shattering the old record.

"It was estimated the ingredients would comprise a 1.375-million calorie gut bomb."

The chief executive of Juicys travelling barbecue catering service, Brett Enright, joined forces with Ovation Food Services co-owner Nick Nicora and a team of helpers to create the record-breaking burger at the Alameda County Fair on Saturday.

"The barbecue was Enright's pride and joy, a massive trailer (the Outlaw Grill) that pops open into a massive food-preparation station with an elevated cooking platform," The Tribune said.

"The rig spends 11 months a year on the road ... (but) the burger was its most challenging project to date."

When the burger was finally ready 15 hours later (not exactly fast food), onlookers paid 99 cents for a portion. The money was donated to a community food bank.

The previous record for a burger was 590 pounds.