The European Union's internal market chief said on Tuesday it was not up to Brussels to comment on Elon Musk's acquisition of the social media site Twitter, but recalled that the bloc now has strict rules for online platforms to tackle illegal content.

"It will be up to Twitter to adapt themselves ... to our rules," Thierry Breton told Reuters and one other media outlet on the deal sealed by Tesla's chief executive to buy Twitter Inc. for $44 billion.

"I think Elon Musk knows Europe very well. He knows very well that we have some rules for the automotive industry ... and he understands that. So in Europe, in order to protect freedom of speech and to protect individuals, any companies will have to fulfill this obligation."

Musk's $44 billion cash deal to buy Twitter lit a fire under tech stocks, and broader equity markets, stalling a selloff that had threatened to take hold.

Asian stocks rallied, taking their cue from Wall Street, and European shares are tipped to open over 1% higher.

Yet the headwinds that grabbed market attention on Monday have not gone away and will continue to test the bounceback.

Let's start with Russia. Foreign minister Sergei Lavrov on Tuesday warned the world not to underestimate the considerable risks of nuclear conflict.

Then, central banks. The European Central Bank's Martins Kazaks joined a chorus of policymakers calling for a swift exit from stimulus, suggesting the ECB should raise rates soon and has room for up to three hikes this year.

Finally, China. Three-quarters of Beijing's 22 million people lined up for COVID-19 tests on Tuesday, as authorities in the Chinese capital raced to stamp out an outbreak.

Fears of the kind of city-wide lockdown that has shrouded Shanghai for a month are raising concerns for the world's second-biggest economy. Any slowdown will no doubt ripple out more widely.

Such worries have pummelled the yuan, pushing it 3.5% lower this month. It got minimal marginal respite from the central bank's pledge on Monday to cut the amount of foreign exchange banks must hold as reserves.

The session ahead will be dominated by earnings. In the European banking landscape, HSBC stood out with a 27% Q1 profit drop which contrasted with the resilience displayed by UBS and Santander.

Amazon.com Inc founder Jeff Bezos has asked in a post on Twitter if Elon Musk's $44 billion cash deal to buy Twitter gives China "a bit of leverage over the town square".

Twitter is blocked in China, where Musk, the world's richest person, has key business interests.

Musk, who calls himself a free speech absolutist and has criticised Twitter's content moderation policy, reached a deal on Monday to buy the social media platform.

Political activists expect that Musk's ownership of Twitter will mean less moderation and reinstatement of banned individuals including former U.S. President Donald Trump.

There are also questions on what the deal will mean for Twitter's China content policy as Musk's Tesla relies heavily on China for production and vehicle sales.

"Did the Chinese government just gain a bit of leverage over the town square?" Bezos tweeted late on Monday.

"My own answer to this question is probably not. The more likely outcome in this regard is complexity in China for Tesla, rather than censorship at Twitter," he later tweeted.