April 30 (Reuters) - Worley's top shareholder, Dubai-based engineering and consulting firm Sidara, has sold a 19% stake in a block trade, the Australian engineering firm said on Tuesday, sending its shares tumbling 7.5%.

Shares of the company settled at A$15.09 apiece, their lowest closing level since early February, while the broader benchmark index ended 0.4% higher.

The deal is worth A$1.63 billion based on the stock's closing level of A$16.310, as per Reuters' calculations.

Worley did not provide further details on the stake sale.

Following the deal, Sidara, formerly known as Dar Group, will no longer be a substantial shareholder in Worley, the former said in a statement without providing details.

"We think the sell-down should come as a relief to Worley's Board and management," RBC Capital Markets analysts said in a note.

Dar operates primarily in building and transportation projects, which provide minimal synergy with Worley's focus on the energy, chemicals and resources sectors, they said.

($1 = 1.5244 Australian dollars)

(Reporting by John Biju and Sameer Manekar in Bengaluru; Editing by Rashmi Aich and Sonia Cheema)