(REUTERS) - A massive fire burned several blocks of boardwalk and businesses on Thursday in Seaside Park, New Jersey, a shore town that was still rebuilding from damage caused by Hurricane Sandy.

New Jersey Governor Chris Christie said 20 businesses had been damaged in a six-block length of the boardwalk and firefighters were struggling to contain the blaze.

"I told my staff, 'I feel like I want to throw up'," Mr Christie told a televised news conference, referring to the effort to rebuild after the massive October 2012 storm. "It is just unthinkable."

The cause of the fire, which sent clouds of smoke streaming north and east under a stiff 56kmh wind, was unknown, Mr Christie said.

Minor injuries were reported to firefighters, the governor said.

Mr John Saaddy, a business owner in nearby Seaside Heights, New Jersey, told CNN the fire had spread by racing through a "fire highway" under the boardwalk.