Boris Johnson chairs his first Cabinet meeting on Thursday after a drastic overhaul

Premier Li Keqiang urged deeper political mutual trust and expanded pragmatic cooperation between China and Britain as he congratulated Boris Johnson on Wednesday on becoming the country's new prime minister.

In a congratulatory letter published on Thursday, Li said ties between China and Britain have maintained a good momentum in recent years with close high-level bilateral exchanges and fruitful cooperation in various areas.

The premier voiced his appreciation to Johnson for his efforts in deepening bilateral ties during his tenures as London mayor and foreign secretary.

Li said China attaches importance to relations with Britain, and he is ready to work together with Johnson to continue with the Golden Era of the bilateral relations and promote the steady growth of the ties.

In London, Johnson gathered his top team around him for the first time on Thursday for a Cabinet meeting that sent a clear message to the European Union that Britain is deadly serious about leaving the bloc on or before the scheduled Oct 31 deadline.

After the meeting, Johnson headed across the road, from 10 Downing Street to the Houses of Parliament, where he addressed MPs and set out his vision for the future, receiving expected criticism from the opposition and some members of his own party, and warm support from others.

On both occasions, Johnson reiterated his commitment to the Oct 31 deadline, which, he told his ministers during their early-morning Cabinet meeting, left his government with "a momentous task ahead".

Johnson's Cabinet is radically different from the one that supported former prime minister Theresa May. Hers comprised ministers with a relatively wide range of Brexit viewpoints. Seventeen members of May's old team-more than half-either resigned or were sacked within a few hours of him taking over as prime minister on Wednesday afternoon. Among them was Jeremy Hunt, May's foreign secretary and Johnson's recent rival for leadership of the Conservative Party.

Leading Brexiteers now have all the key roles at Parliament's highest level, including Sajid Javid, who is the new chancellor of the exchequer; Dominic Raab, who is now foreign secretary; and Priti Patel, who takes over as home secretary. Other key appointments include Liz Truss, who becomes international trade secretary, and Jacob Rees-Mogg, who Johnson declared leader of the House of Commons.

The new prime minister told members of his Cabinet, which he claimed respects the "depth and breadth of talent in our extraordinary party", that they are at a "pivotal moment in our country's history".

"We are now committed, all of us, to leaving the European Union on Oct 31, or indeed earlier. No ifs, no buts, but we are not going to wait until Oct 31 to get on with a fantastic new agenda for our country, and that means delivering the priorities of the people."

In his speech before Parliament, Johnson said he has also asked the independent expert body called the Migration Advisory Committee to come up with a new plan for the nation's immigration system, effectively scrapping planned changes to the UK's visa rules that had been in the pipeline. He also said officials currently working in Brussels will be "unshackled" so they can work on potential trade deals with non-EU nations.

Sky News claimed Johnson's "ruthless cull" of May's supporters from his Cabinet has provoked anger among many Conservative Party MPs.

And Scotland's first minister, Nicola Sturgeon, has written an open letter to Johnson, saying EU-supporting Scotland must have an alternative option to his Brexit plans. She said she may trigger another referendum among Scottish voters on whether the nation should leave the UK.