Pfizer said it could file for US authorisation of the Covid-19 vaccine it is developing with German partner BioNTech as early as late November.

That would suggest it is possible a vaccine could be available in the United States this year.

The timeline makes it unlikely a vaccine will be available before the US election as President Donald Trump has promised.

Pfizer said it may say if the vaccine is effective as soon as this month based on its 40,000 person clinical trial but that it also needs safety data that will not be available until next month.

The Pfizer news, published in a letter from its chief executive on its website, lifted the US stock market and the company's shares.

Shares were up slightly in rival vaccine maker Moderna Inc, which is close to Pfizer in its vaccine development.

"So let me be clear, assuming positive data, Pfizer will apply for Emergency Authorization Use in the US soon after the safety milestone is achieved in the third week of November," Pfizer Chief Executive Albert Bourla said.

Mr Trump has said repeatedly that there would be a vaccine available before the election, but health officials and companies had only said that data might be available this month.

The possibility of further delays was raised after trials for two rival vaccines were put on hold in the United States this fall.

The president's rush to a vaccine has also raised concerns that the US Food and Drug Administration, acting in haste, might not conduct an adequate review of the vaccine.

US health officials have sought to assuage those concerns out of fear that not enough Americans would take a vaccine early on.

Earlier this month, the FDA formalised a requirement that the vaccine makers collect two months of safety data on one-half of trial participants.

Pfizer has been trying to demonstrate that its decision-making is being driven by science rather than politics, Mizuho analyst Vamil Divan said.

"Just getting it to the market is only a small part of it," Mr Divan said.

"People should actually be willing to take it. And the polling shows us that lot of people are reluctant to take it because they think it's not just being driven strictly by the science," he said.

Pfizer's comments on its timeline raise the possibility of US authorisation of a coronavirus vaccine this year, a key step in controlling the Covid-19 pandemic, which has killed more than a million people and ravaged the global economy.

Moderna could also apply for an emergency use authorisation (EUA) this year. It has said that it may have interim data on its 30,000 person trial as soon as November.

Both companies are also applying for approval in Europe, where they are racing against AstraZeneca.

AstraZeneca's US trial has been on hold since September.

Another US trial of a candidate from Johnson & Johnson was paused earlier this week.

After the FDA announced the two-month requirement on 6 October, which was approved by the White House but undercut the likelihood of a vaccine before voters go to polls on 3 November, Mr Trump called the move a "political hit job".