The blast ripped off the roof of the No. 37 bus, strewing wreckage and body parts across the street. Witnesses said the explosion occurred just after the bus stopped in the hilltop neighborhood Carmelia at 2:17 p.m.
Officials said because of the hour, the bus would have been packed with students from the nearby University of Haifa.
There was no immediate reaction from Israel or the Palestinian Authority.
``This is a terror attack,'' said Haifa police chief Yaacov Borovsky. ``We are talking about suicide bomber.''
Some Israeli media reports put the death toll as high as 11. ``There are dozens of casualties, among them seriously injured,'' Avi Zohar, a rescues services spokesman, told Israeli television. At least two dozen were injured.
``I suddenly heard a huge explosion and all the lights in my beauty parlor broke,'' said beautician Ronen Levy. ``I am still in shock.''
The roof of the bus was destroyed and a fire left the bus a skeleton of charred and twisted metal.
It was the first terror attack in Israel since Jan. 5, when a pair of suicide bombers killed 23 people in Tel Aviv. In the past, such attacks have brought on tough Israeli military responses.
Abdel Aziz Rantisi, a spokesman for the militant Hamas group, praised the attack but did not claim responsibility. ``We will not stop our resistance,'' he said. ``We are not going to give up in the face of the daily killing'' of Palestinians.
The attack comes days after the establishment of a new, right-wing government in Israel. Some of the key Cabinet ministers have in the past called for the expulsion of Yasser Arafat, whom Israel accuses of sponsoring terror attacks.
It also coincides with a two-week-old Israeli military offensive against Hamas strongholds in the Gaza Strip in which dozens of Palestinians have been killed, including some civilians.
