Tsunami warning after a coastal earthquake: what to do?

A tsunami is a series of fast-moving waves, usually triggered by an undersea earthquake, landslide or volcanic eruption. Near the source, the first wave can arrive within minutes of the shaking, sometimes before any official warning is issued. If you are on the coast and feel strong or prolonged shaking, treat it as a natural tsunami warning and act at once.

Emergency warning

If you are in immediate danger, call your local emergency services now. Do not call to ask whether a tsunami is coming; use official alerts, sirens, radio or emergency apps for that information, and keep phone lines free for people in danger.

What is happening

Earthquakes that last longer than about 20 seconds, or that are strong enough to make standing difficult, can generate a tsunami. The water may first pull back from the shore, exposing the seabed, but this is not always the case. Waves can travel faster than a person can run and can arrive as a wall of water, a rapid rise, or a series of surges over many hours.

What to do first

1. Move immediately. Head inland or to high ground without waiting for a siren or phone alert. Do not stop to collect belongings.
2. Go on foot if you can. Roads may be blocked, jammed or damaged, and driving can trap you in low-lying areas.
3. Aim for height or distance. Get at least 30 m (100 ft) above sea level, or well inland beyond the expected inundation zone. Follow local evacuation route signs if they exist.
4. Avoid rivers, harbors and estuaries. Tsunami waves can travel far upriver and surge into ports.
5. Help others if it is safe. Warn nearby people, especially children and anyone who may not hear alerts, but do not delay your own evacuation.
6. Stay put until officials say it is safe. Tsunami waves can continue for many hours, and later waves are often larger than the first.

What NOT to do

• Do not go to the beach, pier or harbor to watch the water recede or the waves arrive.
• Do not assume the danger has passed after one wave.
• Do not return to the coast until authorities issue an all-clear.
• Do not rely on a single source; if you feel shaking, act even if no alert has arrived.
• Do not shelter in a basement or underground car park near the coast.

When to call for help

Call emergency services only if someone is injured, trapped, missing or in immediate danger. Report your location clearly and follow instructions from responders. If you are safe, avoid non-urgent calls so lines stay open.

What to monitor

Keep listening to official emergency broadcasts, sirens and local authority messages. Watch for aftershocks, which can cause further damage, and for changes in the sea such as unusual withdrawal or a loud roar. Follow instructions about when and where it is safe to return.

How to prevent harm

Know your local evacuation routes and the nearest high ground before an emergency. Keep a battery-powered radio and a charged phone, and agree a family meeting point inland. If you live or work in a tsunami zone, practice the route so you can leave without thinking.

In short: strong or long shaking at the coast means move inland or uphill immediately, stay there, and wait for the official all-clear.

This is general information and not a substitute for professional emergency advice. In an emergency, call your local emergency services immediately.