Baloise Holding AG has become one of the most-discussed takeover candidates in the European financial sector, after agitation by an activist investor triggered top industry players to take fresh looks at the Swiss insurer.

Zurich Insurance Group AG, Axa SA and Allianz SE are among parties that have been studying whether they would want to bid for Baloise or parts of its business if they come up for sale, the people said. Some of them have spoken to potential advisers as they conduct a preliminary evaluation of the merits and feasibility of a deal, according to the people, who asked not to be identified because the information is private.