Emily whipped up waves in the popular resort of Cancun
Strong winds have felled trees, flooded streets and knocked out power and telephone lines in areas along the coastline popular with tourists.
Emily passed 160km (100 miles) to the south of Jamaica, but left at least four dead after rains caused flooding.
The storm weakened as it moved towards the Gulf of Mexico, but forecasters say Emily could strengthen before reaching Mexico's north-east coast.
Oil rigs have been evacuated and production suspended.
Two pilots died in the Gulf of Mexico when their helicopter crashed during an evacuation of a rig.
Mass evacuation
The second major storm of the season hit Mexico's coast as a category four hurricane - the second highest on the scale of intensity - with winds of 215km/h (135mph).
The US-based National Hurricane Center said the storm made landfall just north of Tulum at 0230 on Monday (0630 GMT), with the eye of the storm passing over the island of Cozumel.
The resort city of Playa del Carmen was also among the most affected areas.
Tens of thousands of tourists and locals were evacuated from the region before Emily's arrival.
About 30,000 tourists were moved inland to better-protected hotels, or packed into emergency shelters in community centres and schools.
Cancun's international airport was closed.
Jamaica battered
Emily is expected to make landfall again in north-eastern Mexico or southern Texas, on Tuesday night.
Jamaica was spared a direct hit, but the island still suffered flooding and landslides. About 70,000 households lost power and several homes and roads were washed away.
The bodies of a man, woman and two children were found inside a car swept over a cliff by flood water, Jamaican police said.
The Cayman Islands also felt the force of the storm early on Sunday.
Last week, Emily battered the eastern Caribbean island of Grenada, leaving one person dead.
Emily comes less than a week after Hurricane Dennis caused more than two dozen deaths as it rampaged through Haiti, Jamaica, Cuba and Florida.
Have you been affected by Hurricane Emily? Send us your experiences using the form below. If you have any pictures of the hurricane's impact you can send them to yourpics@bbc.co.uk.
The following comments reflect the balance of opinion we have received so far:
We had been vacationing in the Riviera Maya before it was evacuated. I just read a news report that the roof of the hotel lobby had blown off and windows had been shattered. We are so sad about the destruction of this beautiful place that we had just enjoyed so much. We are praying for the people of Mexico.
Nicole, Russell, KY
By this weekend it seems it will be business as usual
Mark Temple, Houston, TX
I was in the resort strip of Playa del Carmen as of Saturday night, but luckily was able to leave before the airport shutdown. Before I left, the entire resort area and town was preparing, boarding up windows, evacuating the area. There were the beginnings of a storm taking place and waves were extremely choppy compared to the normal there.
Ben Kelso, Toronto, Canada
I returned from Mexico on Saturday morning. Nineteen of my friends are still out there. Having spoken to them, most of them have been put up into gymnasiums or colleges. As far as I am aware, everyone is okay but are frightened by the experience.
Phil, London
My girlfriend is staying at a Spanish school near Cancun. She sat the storm out in the school house with about 8 other students. She said it was very loud and scary, but they were all fine, except for the loss of all but one TV channel.
Paul C Dunn, London
We have been taking it pretty calmly. Even though others have been preparing by taping up windows, buying water, etc, my family has been going on with life quite normally. I even went swimming today. There are rumours that the local schools may be opened up as public shelters, should the need arise.
Rene Hinojosa, Alice, Texas
By Saturday night a curfew had been declared and everyone was inside waiting
Elaine, George Town, Grand Cayman
My Godmother and her boyfriend are staying in the Marriott Hotel in Cancun. We phoned them yesterday before the storm, they were to be taken downstairs into the ballroom with all the other guests at about midnight their time, to wait out the storm. I hope she is OK. We are awaiting their txt message.
Rebecca Greaves, Tockwith, York, England
This year has been real hectic here in the Caribbean. Last year was incredible with four big hurricanes going through; this year we have narrowly avoided these latest five. We were hit hard by Hurricane Lenny in 2001, since then we are simply praying and keeping alert. These hurricanes are getting worse, and if global warming is true, then we are going to get more of these. We here in St Kitt's are as prepared as we are going to be. It seems that no amount of preparation, prepares for the emotional and mental shock of actually experiencing one of Nature's wonders and terrors.
Jason Graves, St Kitt's, West Indies (originally from the UK)
Stephen, my nephew, and his girlfriend Ellie are on holiday in Mexico and have been evacuated inland. They have only the clothes they were wearing and we have not heard anything from them for some time as they need to preserve the phone battery.
Stephen Saberton, Pymoor, Ely, Cambs, England
I live in Edinburg, about 60 miles west of Brownsville TX. We are getting worried that the path of Emily may come within 50 miles of Brownsville and we are braced for the threat of flooding rain, heavy winds and tornados. We have already bought bottled water, canned food and other supplies. The locals are pretty laid back about it, some were out mowing their lawns this morning and nobody on my street has boarded up their windows or taken any other visible precautions.
Brian Edwards, Edinburg, Texas, USA
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The outer bands of the Category 4 storm Hurricane Emily started to affect Jamaica shortly before 8:00am Saturday. Increasing winds and rain swept the island nation throughout the afternoon as the eye of the storm passed 100 miles off the southern coast. Utility poles were downed and storm debris closed the seaside highway to the international airport. Other roads were reported closed as well. 

While islanders did not get through the two storms unscathed, and 4 people were left dead, the Land and Environment Minister Dean Peart told reporters, "Mercifully, Jamaica was spared the worst".

Buses were sent by officials to southern coastal areas to evacuate residents from the flood prone region, but most refused to leave and preferred to ride it out beside 8 foot waves that pounded areas of the coast line. Wind gusts of 155 mph doubled over palm trees in the capital city of Kingston.

At a southern penninsula seaside fishing villiage, Port Royal residents boarded up and prepared for the worst again, as surfers gathered nearby to take on the challenge of 15 to 18 foot waves. "If I'm going to die, it's going to be right here," said a local resident Gordon Murphy, 39, with his 2-year-old son. "What's next?" he joked, "Hurricane Franklin?"

Many shops and businesses stayed open as long as they could, classifying it as another inconvenience despite its near Category 5 strength. Instead of the possible disaster that many prepared for, by late afternoon, Emily had all but disappeared. Light scattered showers in some areas of the island were the only remnant, as residents went about their lives after the second hurricane scare in as many weeks.

Supplies that many stocked for Dennis and Emily may yet be put to use. Many wonder what storms are yet to come. Authorities say this will be one of the most active hurricane seasons in history. Emily was the strongest and earliest to form this year since records, dating back to 1860, have been kept.

Earlier, Emily stuck Grenada on Thursday with nearly a direct hit. A national disaster was called the day after its winds ravaged hundreds of homes and killed at least one man.