President Donald Trump's administration has been savaged by two leading members of the US scientific community over "alternative" facts, climate change, gagging orders and the travel ban.

Professor Barbara Schaal, president of the American Association for the Advancement of Science (AAAS), and colleague Dr Rush Holt stressed the importance of unrestricted international travel for scientists who need to collaborate on projects.

They also spoke out strongly against the apparent willingness of US government officials to adopt an Orwellian approach to factual evidence, down-play the importance of climate change and restrict public access to information.

Prof Schaal, a former scientific adviser to ex-president Barack Obama, said: "The fact that there could be a conversation about alternative facts is deeply disturbing.

"This kind of conversation where evidence is discarded, where it's modified, where it's morphed, where it's discounted, is very, very concerning."

The row over "alternative facts" blew up after the term was coined by Trump adviser Kellyanne Conway. It followed press secretary Sean Spicer's inaccurate description of the President's inauguration crowd as "the largest ever".

A number of other allegedly unfounded claims made by the Trump administration have also come in for strong criticism.

Prof Schaal urged her fellow scientists to "push back" against alternative facts.

"Every time there's something that's wrong its very important that we just say 'this is not true, this is false'," she said.

Dr Holt, AAAS chief executive and executive publisher of the prestigious Science family of scientific journals, also hit out at the twisting of evidence, saying: "When officials use phrases like alternative facts you know you've got a problem."

Both were speaking at the launch of this year's AAAS conference in Boston, Massachusetts, the world's biggest general science meeting.

On President Trump's attempts to prevent people from seven Muslim countries travelling to the US, Dr Rush said: "I'm sure that the travel ban .. was not meant to have anything to do with science.

"But I think that shows an ignorance of the way science works. No one stopped to think about the implications of this for science."

Prof Schaal referred to early executive orders that told the US Department of Agriculture and Environmental Protection Agency not to communicate information to the public, describing the move as "very chilling".

"That is the antithesis of the way science operates," she added.

She pointed out that science needed to be "on the table" when policy was decided, yet President Trump had not yet appointed a science adviser. Nor were chief scientists yet in post in many government agencies.

"Our concern is that the government won't have the scientific expertise it needs", she said. This would be especially worrying if a crisis occurred such as the Deepwater Horizon oil spill or the Fukushima nuclear disaster in Japan.

Another major cause for concern was how the administration would deal with the issue of climate change. There are fears of a big shift away from climate science.

Prof Schaal said: "If climate science is shut down it's very important that scientists make a very strong case, a very compelling case, a clear case, that climate science is extraordinarily important for the future of nations and for the future of the globe."

Dr Rush added: "I would say scientists have to redouble their efforts. Sometimes that will require courage. There is as yet no clampdown on climate science in the US government. I would say there has been no indication that it will thrive.

"No-one has said how important climate science is to the wellbeing of current and future generations, so that gives people grounds for concern. Its too important to let biased or uninformed views stop it."