Smoke filled the cabin of an Allegiant Air jet after it landed at a California airport on Monday, forcing coughing passengers to cover their faces with shirts and firefighters to board the plane, authorities said. None of the 150 passengers or six crew members was injured when the plane from Las Vegas landed at Fresno International Airport, Allegiant Air said. As the plane was taxiing in Fresno, it came to an abrupt stop and smoke started to fill the cabin from the front of the aircraft, said passenger Estevan Moreno, 34, a Fresno police officer. "We used our shirts to mask our faces from the smoke," he said. "I was coughing pretty good from it." At one point, the flight crew said they would pass out wet napkins to help passengers cover their mouths, Moreno said, but that didn't happen. After firefighters boarded the aircraft, crew members asked passengers to collect their carry-on items and exit the plane down a set of rear stairs, he said. The airline sent Moreno a $50 voucher for another flight, he said. Allegiant Air blamed the situation on a mechanical problem and said having passengers exit the plane before it reached a gate was done out of an abundance of caution. Federal Aviation Administration officials called it an emergency. Federal officials say passengers were escorted to the terminal.