Baby formula brand The a2 Milk Company may be facing a “please explain” letter from the ASX after its shares rocketed more than 13 per cent on Monday following takeover speculation.

The dual-listed group, which makes a2 Platinum formula and fresh milk, said on Monday it “does not comment on media speculation or rumours” after reports Swiss giant Nestlé is mulling a takeover of a2 Milk, which sent the Kiwi company’s shares up 79¢ to $6.75 each on the ASX. They ended the day at $6.68.