Simon Property Group Inc. on Monday made an unsolicited bid for rival real estate group The Macerich Company as it looks to cement its place in the high-end shopping center market.

Simon is offering $16 billion for Macerich, plus the assumption of $6.4 billion in debt. Macerich, a retail real estate investment trust based in Santa Monica, California, confirmed receipt of the bid on Monday and said that it is reviewing the financial terms with its legal and financial advisers.