Collardi had been CEO at the Swiss private bank since 2009 and Chief Risk Officer Bernhard Hodler will take on the job while the bank evaluates long-term leadership of the group, Julius Baer said in a statement.

Shares in Baer, the biggest listed Swiss private bank, opened down 4.2 percent.

Collardi will join Geneva-based Pictet as a partner and his role will include helping oversee its global wealth management business. With 494 billion Swiss francs (378.5 billion pounds)under management, Pictet is about 25 percent bigger than Baer.

He leaves Baer in good shape. It reported record assets under management of 393 billion francs earlier this month, up 17 percent in the first 10 months of this year, and Hodler, on a call with reporters, said he did not expect major changes in the bank's strategy.

Baer Chairman Daniel Sauter said he only learned of Collardi's resignation over the weekend and said Hodler emerged as the best internal candidate to fill the role, for now.

"Bernhard has been appointed as CEO for the foreseeable future, and as I have said before, the board reviews succession planning on an ongoing basis," Sauter told reporters.

"In time, we will appoint a long-term leadership to the group."

While acknowledging that Collardi's departure was sudden, "there are absolutely no issues" or problems that drove him to quit, he said.

"The bank is in perfect shape," Sauter said.

Analysts, however, said Collardi's exit was a blow.

"The somewhat abrupt departure of Mr. Collardi will be taken very negatively by the market considering his very strong leadership status inside the bank," Baader Helvea's Tomasz Grzelak said in a note.

"In particular, we think that the market will now fear ... a negative string of events, such as (the) departure of other relationship managers or loss of client assets."

Hodler, 58, said he represented continuity.

"I stand for continuity, I stand for stability, I stand for making sure that strategy that has been defined is very clear and we successfully implement over the next years," he said.

Collardi had replaced Johannes de Gier, who had served briefly as interim CEO following the 2008 suicide of Alex Widmer.

At non-listed Pictet Collardi will avoid public shareholder discontent over his pay, which he faced at Baer, including a revolt in 2016 when a group opposed his 6.16 million-franc compensation package.

In 2013, Julius Baer had already reduced Collardi's pay by 11 percent after a non-binding vote in which nearly two-thirds of investors voted against the bank's pay plan for the previous year.

Collardi will become one of six partners at Pictet and work alongside Remy Best, the managing partner who has led the bank's global wealth management business since December 2014.

"His presence will re-affirm our commitment to pursue a strategy of independence, organic growth, and focus on the long term," said Nicolas Pictet, the Geneva bank's senior managing partner, in a separate statement.

(Reporting by John Miller; Editing by Amrutha Gayathri and Susan Fenton)

By John Miller