Vocus shares have jumped as much as 26 per cent after the internet provider opened its books to EQT Infrastructure’s $3.3 billion takeover proposal.

Australia’s fourth largest telecommunications provider on Monday said Stockholm-based private equity firm EQT had made a non-binding indicative proposal of $5.25 for each Vocus share.

The offer represented a 35 per cent premium to the stock’s $3.89 valuation before the start of trade and pushed up the shares to a two-and-a-half year high of $4.90.

At 1110 AEST, shares in Vocus were still 20 per cent higher at $4.665.

Vocus, which owns the iPrimus and Dodo brands, said it had granted non-exclusive due diligence access to EQT and that any formal binding proposal “is likely to take a number of weeks”.

“The board notes that there is no certainty that this process or the indicative proposal will result in an offer for Vocus,” the company said in a release.

“Shareholders do not need to take any action in response to the indicative proposal at this time.”

The offer comes two years after US private equity firm Kohlberg Kravis Roberts and Affinity Equity Partners abandoned their $2.2 billion tug-of-war for Vocus, both dumping bids after being unable to support the buy on the board’s terms.

Vocus is currently attempting to reduce its debt by selling assets, although in 2018 it was forced to retain its NZ businesses CallPlus, 2talk, Orcon, Slingshot, and Flip after talks for a sale fell through.

The company is also being sued by shareholders on allegations its downgraded FY17 guidance misled investors.