MANILA, Philippines -- A member of the University of the Philippines-Diliman Police is in critical condition after unruly gate-crashers pelted students with rocks while forcing their way into the UP Fair in Quezon City early Saturday.

Police Officer 2 Arturo Infanta of the Quezon City Police District's station 9 in Anonas identified the victim as Sergeant Ramon Monterico of the UPDP, a team leader of the UP police force handling security on the fair grounds at the Sunken Garden.

Monterico is confined at the intensive care unit of the Quirino Memorial Medical Center, where he is scheduled to undergo surgery.

?He was hit badly in the head with a large stone. His family badly needs money for the operation,? said Sergeant Jocelyn De Peralta, UPDP desk officer.

The UP Fair is an annual week-long festival that is the highlight of the Diliman Month. It features booths, carnival rides, and nightly concerts.

The violence began when rock star Bamboo began playing the first set of his repertoire after midnight Friday.

Several outsiders, numbering more than 10, caused a commotion when they demanded that they be allowed in, but security personnel denied them entry.

?The youths then tried to break down the perimeter fence and began throwing stones at the concert goers, and one of the rocks hit Monterico badly,? Infanta said.

Fair organizers were forced to cancel the concert in order to avoid further injuries, police added.

Police were also able to arrest two boys aged 16 and 17 who were caught throwing stones.

The teenagers, both residents of Culiat village in Quezon City, have been turned over to social workers, police said.

De Peralta noted that Friday night's crowd was larger than usual as the queue of people at the entrance to the fair grounds was as long as a city block.

She added that the U.P.D.P. had 10 officers manning the grounds, with the help of civilian patrollers or the Special Services Brigade and a mobile car of the QCPD making the rounds.