There's a lot of chatter on Wall Street today about a tech bubble — here's what they are saying

Angela Weiss | AFP | Getty Images

(This story is for CNBC Pro subscribers only). 

As mega-cap tech stocks and high-flying names like Tesla struggled Thursday, Wall Street analysts were worrying about a bubble. 

Tech took a rare breather relative to the rest of the market on Wednesday, with the tech-heavy Nasdaq lagging the Dow Jones Industrial Average and S&P 500. That weakness continued on Thursday morning, with the Nasdaq and major stocks like Apple falling in early trading.

The S&P 500 tech sector is down more than 3%, on pace for worst day since June 11. 

Still the Nasdaq has gained about 34% this year and has closed above its 200-day moving average for 83 consecutive sessions. That consistent strength, along with volatile spikes in some individual stocks, has drawn comparisons to the infamous tech bubble from two decades ago. 

"There is an echo of 1999-2000 visible in markets and market behaviour," capital markets firm Berenberg said in a note to clients.