Previous studies of users with visual impairments access to the web have focused on human-web interaction. This study explores the under investigated area of cross-modal collaborative information seeking (CCIS), that is, the challenges and opportunities that exist in supporting visually impaired (VI) users to take an effective part in collaborative web search tasks with sighted peers. We conducted an observational study to investigate the process with fourteen pairs of VI and sighted users in co-located and distributed settings. The study examined the effects of cross-modal collaborative interaction on the stages of the individual Information Seeking (IS) process. The findings showed that the different stages of the process were performed individually most of the time; however it was observed that some collaboration took place in the results exploration and management stages. The accessibility challenges faced by VI users affected their individual and collaborative interaction and also enforced certain points of collaboration. The paper concludes with some recommendations towards improving the accessibility of cross-modal collaborative search.