A school gymnasium fills with hundreds of students seeking shelter from an earthquake and tsunami, with whistles at the ready in case they are trapped by rubble and need to be rescued.

It was only a drill but the exercise Friday is part of the Haitian government's efforts to improve its capacity to respond to natural disasters, six years after an earthquake in the capital Port-au-Prince killed more than 200,000.

Haiti's second-largest city of Cap Haitien is extremely vulnerable, located on the country's northern coast between two major seismic faults.

"This is only an exercise and you can already see the stress among the people," said Pierre Betonus, a geologist working in the emergency operations center where information about the fictional quake and tsunami streamed in continuously.

"Every decision is significant because the purpose is to save more lives, he said.

Cap Haitien's population is estimated to be about 500,000, but the city has only 23 firefighters.

"It's nothing at all but we will try to do what we can," said fire official Jean Frandy, stationed at the "search and rescue" table in the command center.

A few kilometers away, the streets of downtown were filled with students in school uniforms. As part of the drill, more than 3,700 were ordered to evacuate because of the threat of a tsunami.

"If that happened, we would really be running," laughed Cara Meillandre, moving slowing toward higher ground with her classmates in a single file line.

Although the 16-year-old and her friends were enjoying a morning outside the classroom, Meillandre was nevertheless serious when talking about the risks of living in Cap Haitien.

"Earthquakes are a big problem for us and tsunamis are also a danger here. You could survive an earthquake but be killed by the tsunami," she said.

Under the gaze of UN peacekeepers and police blocking traffic, slow-moving students were herded into the gymnasium and called to order.

"You have to repeat this exercise for years and years, so that it becomes a reflex not only among the children but also the rest of the population," said Mourad Whaba, UN humanitarian coordinator in Haiti.

Church bells rang during the drill to warn residents of danger but they could hardly be heard inside noisy classrooms.

"Sirens to inform people that they have to evacuate must be installed," Whaba said.

The drill involved a total of 4,500 people and educating the population at large will be a huge challenge.

The last big earthquake to hit Cap Haitien, in 1842, killed half of the population.

According to experts, if the 6.7 magnitude earthquake and tsunami in the drill actually struck the city, 46,000 people would be killed, 221,000 would be left homeless and half the city's buildings -- including its port, airport and power plant -- would be destroyed.