Midjourney responded to a request Thursday for a trial with a message saying it could not be provided and to try again another day.

The imagery created using the artificial intelligence platform, particularly those of Trump and the pontiff which went viral, has put a spotlight on the San Francisco-based lab.

"Due to a combination of extraordinary demand and trial abuse we are temporarily disabling free trials until we have our next improvements to the system deployed," Midjourney founder David Holz said in a post this week on the company's Discord channel.

Photo of Pope Francis wearing a puffer Jacket created by AI image generator software Midjourney. (Photo courtesy of social media platform Reddit) 

The service generates realistic-looking images based on written prompts made by users.

It launched in test mode in mid-2022, with the independent lab consistently upgrading the software.

Users have praised a freshly released version of Midjourney for improved realism in produced images.

Along with putting the brakes on new free trials, Midjourney banned certain words, such as "arrested," from being used to prompt image creation.

On Thursday Midjourney denied a request by AFP to generate an image of the former president being arrested in front of Trump Tower in New York.

"The word 'arrested' is banned," a message from Midjourney stated.

"Circumventing this filter to violate our rules may result in your access being revoked."

Billionaire mogul and Twitter owner Elon Musk and a range of experts called on Wednesday for a pause in the development of powerful artificial intelligence systems to allow time to make sure they are safe.

An open letter, signed by more than 1,000 people so far including Musk and Apple co-founder Steve Wozniak, was prompted by the release of artificial intelligence platform GPT-4 from Microsoft-backed firm OpenAI.

Canadian AI pioneer Yoshua Bengio, who signed the letter, warned during a virtual press conference in Montreal that "society is not ready" for this powerful tool, and its possible misuse.

"Let's slow down. Let's make sure that we develop better guardrails," he said.