Suspected communist rebels torched five passenger buses at a terminal in the Philippine capital on Thursday, but no one was hurt in the attack, police said, dpa reported.
The 10 suspects barged into the Victory Liner bus compound in Manila's commercial district of Cubao before dawn and disarmed the security guards.
They then doused one bus with paint thinner and set it on fire, said Senior Superintendent Magtanggol Gatdula, city police chief.
The fire spread to four other buses in the compound.
Gatdula said the suspects introduced themselves as communist rebels, but noted that investigators were not yet discounting the possibility that a labour dispute or extortion was behind the attack.
"We are looking into the possibility of disgruntled employees being behind this," he said. "The firm has dismissed many drivers who got involved in accidents."
One security guard told investigators that the suspects assured the people at the compound that they will not be hurt.
"We are outsiders and we are mad at Victory Liner for not giving us what we want," the guard quoted one of the rebels as telling them.
Communist rebels are known to attack businessmen and companies that refuse to pay "revolutionary taxes," which are a key source of funds for the guerrillas.
In some provinces, even local politicians are forced to pay protection money to the rebels.
The guerrillas have been fighting the Philippine government since the late 1960s, making the movement one of the longest-running leftist insurgencies in Asia.