(Bloomberg) -- The surge in Jimmy Lai’s media company shares faltered on Wednesday following a two-day, 1,100% surge as Hong Kong’s securities regulator warned on the stock and pro-democracy supporters broadened their buying to other firms.

The Securities and Futures Commission said in a statement it was monitoring trading activity related to the stock and advised investors to exercise “extreme caution” when dealing in Next Digital Ltd. shares. The stock was last up 5.5% at HK$1.16, after rising as high as HK$1.96 on Tuesday. It traded last week at 9 H.K. cents.

Buying the stock has become a popular way for the city’s pro-democracy activists to show support for Lai following his arrest on Monday, along with snapping up copies of his Apple Daily newspaper. The high-profile publisher, who has long called for greater democracy in the former British colony, was released on bail early Wednesday after being arrested for foreign collusion under the new national security law.

Other media companies considered independent of government influence have also rallied as activists called in online forums for people to buy “yellow” firms -- a reference to the color of the pro-democracy movement first popularized in protests that erupted in 2014.

Most Kwai Chung Ltd., a satirical media group known for its anti-government stance, climbed as much as 35% further on Wednesday before dropping as much as 32% from Tuesday’s close. Mi Ming Mart Holdings Ltd., founded by former pro-democracy politician Erica Yuen, was 15% higher mid-morning Wednesday after more than doubling on Tuesday. Easy Repay Finance & Investment Ltd. -- chaired by Stephen Shiu Yeuk-yuen, who is an outspoken supporter of the democratic movement -- surged 48% on Wednesday.

Next Digital’s surge has boosted Lai’s wealth, on paper at least. The two-day gain added HK$2.7 billion ($344 million) in value to the shares. The former penny stock was the third-most traded in Hong Kong on Tuesday after internet firms Tencent Holdings Ltd. and Meituan Dianping.

Next Digital said late Tuesday it wasn’t aware of any reason for increase in the volume and share price, according to a Hong Kong stock exchange filing.

©2020 Bloomberg L.P.