A logo of Alibaba Group is seen during Alibaba Group's 11.11 Singles' Day global shopping festival at the company's headquarters in Hangzhou, China, November 11, 2019.

Alibaba will close its order books to institutional investors early for its upcoming secondary listing in Hong Kong, a sign that demand for shares is strong, two sources with direct knowledge of the matter told CNBC.

The e-commerce giant will close its book at 12 p.m. ET on Tuesday, earlier than initially planned, the sources, who wished to remain anonymous because they are not authorized to speak publicly, said. One of the sources who spoke to CNBC said the book will close half a day earlier than originally scheduled.

An Alibaba spokesperson declined to comment when contacted by CNBC.

"The book is well-covered," one source said. "The international offering received strong feedback."

Alibaba got the greenlight from Hong Kong regulators for the secondary listing last week, CNBC previously reported.

News of Alibaba's plans to close the books early was first reported by Reuters.