Two gunmen have been shot dead in Texas at a "draw the prophet" art exhibition and contest that offered a $10,000 prize for the best cartoon of the Prophet Muhammad. The event was attended by the controversial far-right Dutch politician Geert Wilders.

About 20 shots rang out and an unarmed security guard was injured before police opened fire on the gunmen. Members of the public were evacuated amid apparent concerns that the dead gunmen, their car and surrounding areas might be mined with explosives. A bomb squad has been called in and the site is still in lock-down.

The exhibition was organised by Pamela Geller's American Freedom Defense Initiative at the Curtis Culwell Center in Garland. The shootings took place at around 7pm last night Texas time.

Joe Harn, of Garland Police, said: "Because of the situation of what was going on today and the history of what we've been told has happened at other events like this, we are considering their car (is) possibly containing a bomb."

Mayor of Garland Douglas Athas said: "Two men in a car tried to drive into the parking lot, jumped out with automatic rifles. Started firing at an unarmed schools security officer who was hit in the leg. He was transported to the hospital.

"The first suspect was shot immediately. The second was shot and wounded, reached for his backpack and, of course, officers not knowing any idea what was in the backpack, shot him again and he was killed."

He admitted the exhibition was controversial.

"This group wanted to rent it," he said. "There was concern which is why we had heightened security in the area, but we all swear to uphold the constitution, free speech, free assembly and in this case freedom of religion, so they were welcome to use the building."

Twenty minutes before the shooting, a person with the handle @atawaakul and user name Shariah is Light, tweeted: "The bro with me and myself have given bay'ah to Amirul Mu'mineen. May Allah accept us as mujahideen. Make dua #texasattack". The account has been suspended.

Robert Spencer, who runs the website Jihad Watch and was one of the event's organisers, had also received death threats.

Wilders, who in 2009 was banned from entering the UK and labelled an "undesirable person", and who once said: "I don't hate Muslims, I hate Islam," delivered a speech at the event shortly before the attack.

Wilders said: "It is no coincidence that we are in Garland, Texas, tonight. It is here that, three months ago, shortly after the Charlie Hebdo massacre, Islamic activists convened to demand that free speech be curtailed. They want to prohibit cartoons, books and films which they find insulting.

"Our answer is clear: Don't mess with Texas! Don't mess with the free West! Don't mess with our freedom of speech!"

He continued: "I know from my own experience how dangerous it is to stand for this freedom. I know how dangerous it is to speak the truth about Islam.

"I am on death lists of Al-Qaeda and the Pakistani Taliban and terrorists from ISIS because I tell people the truth about Islam. Islam has declared war on us, on our Judeo-Christian civilisation. Islam wants to rob us of the freedoms and liberties. Islam and freedom are totally incompatible.

"I am a politician, but cartoonists, like my good friends the Danish cartoonist Kurt Westergaard and the Swedish artist Lars Vilks, are also on the death list. Both Kurt and Lars have already been the victims of murder attempts.

"Another man on this list was the cartoonist Charb, editor of the French magazine Charlie Hebdo. As we all know, he and nine of his colleagues were murdered last January in Paris by followers of the religion of hate. According to Islamic Sharia law, they were all guilty of the same crime. The crime of depicting Muhammad, the crime of defaming the so-called Prophet of Islam. A crime punishable by death by the religion of death."

After the shootings Geller said she chose the Garland venue because it was where American Muslim leaders held a conference on combating Islamophobia a week after the Charlie Hebdo attacks.