Five people have been arrested during protests at the University of Sydney during which a group of students allegedly stormed into a chemistry lecture hall and clashed with police.

A NSW Police spokesman said five people were being questioned in relation to possible criminal behaviour after they were arrested at the university's Camperdown campus on Tuesday.

University staff voted to strike on Tuesday and Wednesday after failing to negotiate a collective agreement with university management.

National Tertiary Education Union branch president Michael Thomson said the union had been negotiating for seven months without management agreeing to even one clause for a new enterprise agreement.